Undesign client validation

This change removes a layer of abstraction. These validators now just do
what they do now without creating a bunch of intermediate objects.

ModelClientValidationRule has been removed, and client validations
manipulate the attributes collection of a tag directly.

src/Microsoft.AspNetCore.Mvc.Abstractions/ModelBinding/Validation/ClientModelValidationContext.cs

@@ -1,6 +1,8 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System.Collections.Generic;
+
 namespace Microsoft.AspNetCore.Mvc.ModelBinding.Validation
 {
     /// <summary>
@@ -14,12 +16,20 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Validation
         /// <param name="actionContext">The <see cref="ActionContext"/> for validation.</param>
         /// <param name="metadata">The <see cref="ModelMetadata"/> for validation.</param>
         /// <param name="metadataProvider">The <see cref="IModelMetadataProvider"/> to be used in validation.</param>
+        /// <param name="attributes">The attributes dictionary for the HTML tag being rendered.</param>
         public ClientModelValidationContext(
             ActionContext actionContext,
             ModelMetadata metadata,
-            IModelMetadataProvider metadataProvider)
+            IModelMetadataProvider metadataProvider,
+            IDictionary<string, string> attributes)
             : base(actionContext, metadata, metadataProvider)
         {
+            Attributes = attributes;
         }
+
+        /// <summary>
+        /// Gets the attributes dictionary for the HTML tag being rendered.
+        /// </summary>
+        public IDictionary<string, string> Attributes { get; }
     }
 }

src/Microsoft.AspNetCore.Mvc.Abstractions/ModelBinding/Validation/IClientModelValidator.cs

@@ -1,12 +1,10 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
-using System.Collections.Generic;
-
 namespace Microsoft.AspNetCore.Mvc.ModelBinding.Validation
 {
     public interface IClientModelValidator
     {
-        IEnumerable<ModelClientValidationRule> GetClientValidationRules(ClientModelValidationContext context);
+        void AddValidation(ClientModelValidationContext context);
     }
 }

src/Microsoft.AspNetCore.Mvc.Abstractions/ModelBinding/Validation/ModelClientValidationRule.cs

@@ -1,55 +0,0 @@
-// Copyright (c) .NET Foundation. All rights reserved.
-// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
-
-using System;
-using System.Collections.Generic;
-
-namespace Microsoft.AspNetCore.Mvc.ModelBinding.Validation
-{
-    public class ModelClientValidationRule
-    {
-        private readonly Dictionary<string, object> _validationParameters =
-            new Dictionary<string, object>(StringComparer.Ordinal);
-
-        public ModelClientValidationRule(string errorMessage)
-            : this(validationType: string.Empty, errorMessage: errorMessage)
-        {
-            if (errorMessage == null)
-            {
-                throw new ArgumentNullException(nameof(errorMessage));
-            }
-        }
-
-        public ModelClientValidationRule(
-            string validationType,
-            string errorMessage)
-        {
-            if (validationType == null)
-            {
-                throw new ArgumentNullException(nameof(validationType));
-            }
-
-            if (errorMessage == null)
-            {
-                throw new ArgumentNullException(nameof(errorMessage));
-            }
-
-            ValidationType = validationType;
-            ErrorMessage = errorMessage;
-        }
-
-        public string ErrorMessage { get; private set; }
-
-        /// <summary>
-        /// Identifier of the <see cref="ModelClientValidationRule"/>. If client-side validation is enabled, default
-        /// validation attribute generator uses this <see cref="string"/> as part of the generated "data-val"
-        /// attribute name. Must be unique in the set of enabled validation rules.
-        /// </summary>
-        public string ValidationType { get; private set; }
-
-        public IDictionary<string, object> ValidationParameters
-        {
-            get { return _validationParameters; }
-        }
-    }
-}

src/Microsoft.AspNetCore.Mvc.DataAnnotations/Internal/CompareAttributeAdapter.cs

@@ -2,7 +2,6 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Collections.Generic;
 using System.ComponentModel.DataAnnotations;
 using System.Globalization;
 using Microsoft.AspNetCore.Mvc.ModelBinding;
@@ -13,26 +12,24 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
 {
     public class CompareAttributeAdapter : AttributeAdapterBase<CompareAttribute>
     {
+        private readonly string _otherProperty;
+
         public CompareAttributeAdapter(CompareAttribute attribute, IStringLocalizer stringLocalizer)
             : base(new CompareAttributeWrapper(attribute), stringLocalizer)
         {
-            if (attribute == null)
+            _otherProperty = "*." + attribute.OtherProperty;
-            {
-                throw new ArgumentNullException(nameof(attribute));
-            }
         }
 
-        public override IEnumerable<ModelClientValidationRule> GetClientValidationRules(
+        public override void AddValidation(ClientModelValidationContext context)
-            ClientModelValidationContext context)
         {
             if (context == null)
             {
                 throw new ArgumentNullException(nameof(context));
             }
 
-            var errorMessage = GetErrorMessage(context);
+            MergeAttribute(context.Attributes, "data-val", "true");
-            var clientRule = new ModelClientValidationEqualToRule(errorMessage, "*." + Attribute.OtherProperty);
+            MergeAttribute(context.Attributes, "data-val-equalto", GetErrorMessage(context));
-            return new[] { clientRule };
+            MergeAttribute(context.Attributes, "data-val-equalto-other", _otherProperty);
         }
 
         /// <inheritdoc />

src/Microsoft.AspNetCore.Mvc.DataAnnotations/Internal/DataTypeAttributeAdapter.cs

@@ -2,7 +2,6 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Collections.Generic;
 using System.ComponentModel.DataAnnotations;
 using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
 using Microsoft.Extensions.Localization;
@@ -26,18 +25,17 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
             RuleName = ruleName;
         }
 
-        public string RuleName { get; private set; }
+        public string RuleName { get; }
 
-        public override IEnumerable<ModelClientValidationRule> GetClientValidationRules(
+        public override void AddValidation(ClientModelValidationContext context)
-            ClientModelValidationContext context)
         {
             if (context == null)
             {
                 throw new ArgumentNullException(nameof(context));
             }
 
-            var errorMessage = GetErrorMessage(context);
+            MergeAttribute(context.Attributes, "data-val", "true");
-            return new[] { new ModelClientValidationRule(RuleName, errorMessage) };
+            MergeAttribute(context.Attributes, RuleName, GetErrorMessage(context));
         }
 
         /// <inheritdoc/>

src/Microsoft.AspNetCore.Mvc.DataAnnotations/Internal/MaxLengthAttributeAdapter.cs

@@ -2,8 +2,8 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Collections.Generic;
 using System.ComponentModel.DataAnnotations;
+using System.Globalization;
 using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
 using Microsoft.Extensions.Localization;
 
@@ -11,21 +11,24 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
 {
     public class MaxLengthAttributeAdapter : AttributeAdapterBase<MaxLengthAttribute>
     {
+        private readonly string _max;
+
         public MaxLengthAttributeAdapter(MaxLengthAttribute attribute, IStringLocalizer stringLocalizer)
             : base(attribute, stringLocalizer)
         {
+            _max = Attribute.Length.ToString(CultureInfo.InvariantCulture);
         }
 
-        public override IEnumerable<ModelClientValidationRule> GetClientValidationRules(
+        public override void AddValidation(ClientModelValidationContext context)
-            ClientModelValidationContext context)
         {
             if (context == null)
             {
                 throw new ArgumentNullException(nameof(context));
             }
 
-            var message = GetErrorMessage(context);
+            MergeAttribute(context.Attributes, "data-val", "true");
-            return new[] { new ModelClientValidationMaxLengthRule(message, Attribute.Length) };
+            MergeAttribute(context.Attributes, "data-val-maxlength", GetErrorMessage(context));
+            MergeAttribute(context.Attributes, "data-val-maxlength-max", _max);
         }
 
         /// <inheritdoc />

src/Microsoft.AspNetCore.Mvc.DataAnnotations/Internal/MinLengthAttributeAdapter.cs

@@ -2,8 +2,8 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Collections.Generic;
 using System.ComponentModel.DataAnnotations;
+using System.Globalization;
 using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
 using Microsoft.Extensions.Localization;
 
@@ -11,21 +11,24 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
 {
     public class MinLengthAttributeAdapter : AttributeAdapterBase<MinLengthAttribute>
     {
+        private readonly string _min;
+
         public MinLengthAttributeAdapter(MinLengthAttribute attribute, IStringLocalizer stringLocalizer)
             : base(attribute, stringLocalizer)
         {
+            _min = Attribute.Length.ToString(CultureInfo.InvariantCulture);
         }
 
-        public override IEnumerable<ModelClientValidationRule> GetClientValidationRules(
+        public override void AddValidation(ClientModelValidationContext context)
-            ClientModelValidationContext context)
         {
             if (context == null)
             {
                 throw new ArgumentNullException(nameof(context));
             }
 
-            var message = GetErrorMessage(context);
+            MergeAttribute(context.Attributes, "data-val", "true");
-            return new[] { new ModelClientValidationMinLengthRule(message, Attribute.Length) };
+            MergeAttribute(context.Attributes, "data-val-minlength", GetErrorMessage(context));
+            MergeAttribute(context.Attributes, "data-val-minlength-min", _min);
         }
 
         /// <inheritdoc />

src/Microsoft.AspNetCore.Mvc.DataAnnotations/Internal/ModelClientValidationEqualToRule.cs

@@ -1,30 +0,0 @@
-// Copyright (c) .NET Foundation. All rights reserved.
-// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
-
-using System;
-using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
-
-namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
-{
-    /// <summary>
-    /// Represents client side validation rule that determines if two values are equal.
-    /// </summary>
-    public class ModelClientValidationEqualToRule : ModelClientValidationRule
-    {
-        private const string EqualToValidationType = "equalto";
-        private const string EqualToValidationParameter = "other";
-
-        public ModelClientValidationEqualToRule(
-            string errorMessage,
-            object other)
-            : base(EqualToValidationType, errorMessage)
-        {
-            if (other == null)
-            {
-                throw new ArgumentNullException(nameof(other));
-            }
-
-            ValidationParameters[EqualToValidationParameter] = other;
-        }
-    }
-}

src/Microsoft.AspNetCore.Mvc.DataAnnotations/Internal/ModelClientValidationMaxLengthRule.cs

@@ -1,19 +0,0 @@
-// Copyright (c) .NET Foundation. All rights reserved.
-// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
-
-using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
-
-namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
-{
-    public class ModelClientValidationMaxLengthRule : ModelClientValidationRule
-    {
-        private const string MaxLengthValidationType = "maxlength";
-        private const string MaxLengthValidationParameter = "max";
-
-        public ModelClientValidationMaxLengthRule(string errorMessage, int maximumLength)
-            : base(MaxLengthValidationType, errorMessage)
-        {
-            ValidationParameters[MaxLengthValidationParameter] = maximumLength;
-        }
-    }
-}

src/Microsoft.AspNetCore.Mvc.DataAnnotations/Internal/ModelClientValidationMinLengthRule.cs

@@ -1,19 +0,0 @@
-// Copyright (c) .NET Foundation. All rights reserved.
-// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
-
-using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
-
-namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
-{
-    public class ModelClientValidationMinLengthRule : ModelClientValidationRule
-    {
-        private const string MinLengthValidationType = "minlength";
-        private const string MinLengthValidationParameter = "min";
-
-        public ModelClientValidationMinLengthRule(string errorMessage, int minimumLength)
-            : base(MinLengthValidationType, errorMessage)
-        {
-            ValidationParameters[MinLengthValidationParameter] = minimumLength;
-        }
-    }
-}

src/Microsoft.AspNetCore.Mvc.DataAnnotations/Internal/ModelClientValidationNumericRule.cs

@@ -1,25 +0,0 @@
-// Copyright (c) .NET Foundation. All rights reserved.
-// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
-
-using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
-
-namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
-{
-    /// <summary>
-    /// This is a <see cref="ModelClientValidationRule"/> for numeric values.
-    /// </summary>
-    public class ModelClientValidationNumericRule : ModelClientValidationRule
-    {
-        private const string NumericValidationType = "number";
-
-        /// <summary>
-        /// Creates an instance of <see cref="ModelClientValidationNumericRule"/>
-        /// with the given <paramref name="errorMessage"/>.
-        /// </summary>
-        /// <param name="errorMessage">The error message to be displayed.</param>
-        public ModelClientValidationNumericRule(string errorMessage)
-            : base(NumericValidationType, errorMessage)
-        {
-        }
-    }
-}

src/Microsoft.AspNetCore.Mvc.DataAnnotations/Internal/ModelClientValidationRangeRule.cs

@@ -1,35 +0,0 @@
-// Copyright (c) .NET Foundation. All rights reserved.
-// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
-
-using System;
-using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
-
-namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
-{
-    public class ModelClientValidationRangeRule : ModelClientValidationRule
-    {
-        private const string RangeValidationType = "range";
-        private const string MinValidationParameter = "min";
-        private const string MaxValidationParameter = "max";
-
-        public ModelClientValidationRangeRule(
-            string errorMessage,
-            object minValue,
-            object maxValue)
-            : base(RangeValidationType, errorMessage)
-        {
-            if (minValue == null)
-            {
-                throw new ArgumentNullException(nameof(minValue));
-            }
-
-            if (maxValue == null)
-            {
-                throw new ArgumentNullException(nameof(maxValue));
-            }
-
-            ValidationParameters[MinValidationParameter] = minValue;
-            ValidationParameters[MaxValidationParameter] = maxValue;
-        }
-    }
-}

src/Microsoft.AspNetCore.Mvc.DataAnnotations/Internal/ModelClientValidationRegexRule.cs

@@ -1,19 +0,0 @@
-// Copyright (c) .NET Foundation. All rights reserved.
-// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
-
-using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
-
-namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
-{
-    public class ModelClientValidationRegexRule : ModelClientValidationRule
-    {
-        private const string RegexValidationType = "regex";
-        private const string RegexValidationRuleName = "pattern";
-
-        public ModelClientValidationRegexRule(string errorMessage, string pattern)
-            : base(RegexValidationType, errorMessage)
-        {
-            ValidationParameters.Add(RegexValidationRuleName, pattern);
-        }
-    }
-}

src/Microsoft.AspNetCore.Mvc.DataAnnotations/Internal/ModelClientValidationRequiredRule.cs

@@ -1,17 +0,0 @@
-// Copyright (c) .NET Foundation. All rights reserved.
-// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
-
-using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
-
-namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
-{
-    public class ModelClientValidationRequiredRule : ModelClientValidationRule
-    {
-        private const string RequiredValidationType = "required";
-
-        public ModelClientValidationRequiredRule(string errorMessage) :
-            base(RequiredValidationType, errorMessage)
-        {
-        }
-    }
-}

src/Microsoft.AspNetCore.Mvc.DataAnnotations/Internal/ModelClientValidationStringLengthRule.cs

@@ -1,28 +0,0 @@
-// Copyright (c) .NET Foundation. All rights reserved.
-// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
-
-using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
-
-namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
-{
-    public class ModelClientValidationStringLengthRule : ModelClientValidationRule
-    {
-        private const string LengthValidationType = "length";
-        private const string MinValidationParameter = "min";
-        private const string MaxValidationParameter = "max";
-
-        public ModelClientValidationStringLengthRule(string errorMessage, int minimumLength, int maximumLength)
-            : base(LengthValidationType, errorMessage)
-        {
-            if (minimumLength != 0)
-            {
-                ValidationParameters[MinValidationParameter] = minimumLength;
-            }
-
-            if (maximumLength != int.MaxValue)
-            {
-                ValidationParameters[MaxValidationParameter] = maximumLength;
-            }
-        }
-    }
-}

src/Microsoft.AspNetCore.Mvc.DataAnnotations/Internal/NumericClientModelValidator.cs

@@ -15,14 +15,26 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
     public class NumericClientModelValidator : IClientModelValidator
     {
         /// <inheritdoc />
-        public IEnumerable<ModelClientValidationRule> GetClientValidationRules(ClientModelValidationContext context)
+        public void AddValidation(ClientModelValidationContext context)
         {
             if (context == null)
             {
                 throw new ArgumentNullException(nameof(context));
             }
 
-            return new[] { new ModelClientValidationNumericRule(GetErrorMessage(context.ModelMetadata)) };
+            MergeAttribute(context.Attributes, "data-val", "true");
+            MergeAttribute(context.Attributes, "data-val-number", GetErrorMessage(context.ModelMetadata));
+        }
+
+        private static bool MergeAttribute(IDictionary<string, string> attributes, string key, string value)
+        {
+            if (attributes.ContainsKey(key))
+            {
+                return false;
+            }
+
+            attributes.Add(key, value);
+            return true;
         }
 
         private string GetErrorMessage(ModelMetadata modelMetadata)

src/Microsoft.AspNetCore.Mvc.DataAnnotations/Internal/RangeAttributeAdapter.cs

@@ -2,8 +2,8 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Collections.Generic;
 using System.ComponentModel.DataAnnotations;
+using System.Globalization;
 using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
 using Microsoft.Extensions.Localization;
 
@@ -11,26 +11,34 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
 {
     public class RangeAttributeAdapter : AttributeAdapterBase<RangeAttribute>
     {
+        private readonly string _max;
+        private readonly string _min;
+
         public RangeAttributeAdapter(RangeAttribute attribute, IStringLocalizer stringLocalizer)
             : base(attribute, stringLocalizer)
         {
+            // This will trigger the conversion of Attribute.Minimum and Attribute.Maximum.
+            // This is needed, because the attribute is stateful and will convert from a string like
+            // "100m" to the decimal value 100.
+            //
+            // Validate a randomly selected number.
+            attribute.IsValid(3); 
+
+            _max = Convert.ToString(Attribute.Maximum, CultureInfo.InvariantCulture);
+            _min = Convert.ToString(Attribute.Minimum, CultureInfo.InvariantCulture);
         }
 
-        public override IEnumerable<ModelClientValidationRule> GetClientValidationRules(
+        public override void AddValidation(ClientModelValidationContext context)
-            ClientModelValidationContext context)
         {
             if (context == null)
             {
                 throw new ArgumentNullException(nameof(context));
             }
 
-            // TODO: Only calling this so Minimum and Maximum convert. Caused by a bug in CoreFx.
+            MergeAttribute(context.Attributes, "data-val", "true");
-            Attribute.IsValid(null);
+            MergeAttribute(context.Attributes, "data-val-range", GetErrorMessage(context));
-
+            MergeAttribute(context.Attributes, "data-val-range-max", _max);
-            var errorMessage = GetErrorMessage(context);
+            MergeAttribute(context.Attributes, "data-val-range-min", _min);
-
-
-            return new[] { new ModelClientValidationRangeRule(errorMessage, Attribute.Minimum, Attribute.Maximum) };
         }
 
         /// <inheritdoc />

src/Microsoft.AspNetCore.Mvc.DataAnnotations/Internal/RegularExpressionAttributeAdapter.cs

@@ -2,7 +2,6 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Collections.Generic;
 using System.ComponentModel.DataAnnotations;
 using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
 using Microsoft.Extensions.Localization;
@@ -16,16 +15,16 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
         {
         }
 
-        public override IEnumerable<ModelClientValidationRule> GetClientValidationRules(
+        public override void AddValidation(ClientModelValidationContext context)
-            ClientModelValidationContext context)
         {
             if (context == null)
             {
                 throw new ArgumentNullException(nameof(context));
             }
 
-            var errorMessage = GetErrorMessage(context);
+            MergeAttribute(context.Attributes, "data-val", "true");
-            return new[] { new ModelClientValidationRegexRule(errorMessage, Attribute.Pattern) };
+            MergeAttribute(context.Attributes, "data-val-regex", GetErrorMessage(context));
+            MergeAttribute(context.Attributes, "data-val-regex-pattern", Attribute.Pattern);
         }
 
         /// <inheritdoc />

src/Microsoft.AspNetCore.Mvc.DataAnnotations/Internal/RequiredAttributeAdapter.cs

@@ -2,7 +2,6 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Collections.Generic;
 using System.ComponentModel.DataAnnotations;
 using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
 using Microsoft.Extensions.Localization;
@@ -16,16 +15,15 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
         {
         }
 
-        public override IEnumerable<ModelClientValidationRule> GetClientValidationRules(
+        public override void AddValidation(ClientModelValidationContext context)
-           ClientModelValidationContext context)
         {
             if (context == null)
             {
                 throw new ArgumentNullException(nameof(context));
             }
 
-            var errorMessage = GetErrorMessage(context);
+            MergeAttribute(context.Attributes, "data-val", "true");
-            return new[] { new ModelClientValidationRequiredRule(errorMessage) };
+            MergeAttribute(context.Attributes, "data-val-required", GetErrorMessage(context));
         }
 
         /// <inheritdoc />

src/Microsoft.AspNetCore.Mvc.DataAnnotations/Internal/StringLengthAttributeAdapter.cs

@@ -2,8 +2,8 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Collections.Generic;
 using System.ComponentModel.DataAnnotations;
+using System.Globalization;
 using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
 using Microsoft.Extensions.Localization;
 
@@ -11,24 +11,36 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
 {
     public class StringLengthAttributeAdapter : AttributeAdapterBase<StringLengthAttribute>
     {
+        private readonly string _max;
+        private readonly string _min;
+
         public StringLengthAttributeAdapter(StringLengthAttribute attribute, IStringLocalizer stringLocalizer)
             : base(attribute, stringLocalizer)
         {
+            _max = Attribute.MaximumLength.ToString(CultureInfo.InvariantCulture);
+            _min = Attribute.MinimumLength.ToString(CultureInfo.InvariantCulture);
         }
 
-        public override IEnumerable<ModelClientValidationRule> GetClientValidationRules(
+        /// <inheritdoc />
-            ClientModelValidationContext context)
+        public override void AddValidation(ClientModelValidationContext context)
         {
             if (context == null)
             {
                 throw new ArgumentNullException(nameof(context));
             }
 
-            var errorMessage = GetErrorMessage(context);
+            MergeAttribute(context.Attributes, "data-val", "true");
-            var rule = new ModelClientValidationStringLengthRule(errorMessage,
+            MergeAttribute(context.Attributes, "data-val-length", GetErrorMessage(context));
-                                                                 Attribute.MinimumLength,
+
-                                                                 Attribute.MaximumLength);
+            if (Attribute.MaximumLength != int.MaxValue)
-            return new[] { rule };
+            {
+                MergeAttribute(context.Attributes, "data-val-length-max", _max);
+            }
+
+            if (Attribute.MinimumLength != 0)
+            {
+                MergeAttribute(context.Attributes, "data-val-length-min", _min);
+            }
         }
 
         /// <inheritdoc />

src/Microsoft.AspNetCore.Mvc.DataAnnotations/Internal/ValidationAttributeAdapterOfTAttribute.cs

@@ -32,14 +32,30 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
         /// <summary>
         /// Gets the <typeparamref name="TAttribute"/> instance.
         /// </summary>
-        public TAttribute Attribute
+        public TAttribute Attribute { get; }
-        {
-            get;
-        }
 
         /// <inheritdoc />
-        public abstract IEnumerable<ModelClientValidationRule> GetClientValidationRules(
+        public abstract void AddValidation(ClientModelValidationContext context);
-            ClientModelValidationContext context);
+
+        /// <summary>
+        /// Adds the given <paramref name="key"/> and <paramref name="value"/> into
+        /// <paramref name="attributes"/> if <paramref name="attributes"/> does not contain a value for
+        /// <paramref name="key"/>.
+        /// </summary>
+        /// <param name="attributes">The HTML attributes dictionary.</param>
+        /// <param name="key">The attribute key.</param>
+        /// <param name="value">The attribute value.</param>
+        /// <returns><c>true</c> if an attribute was added, otherwise <c>false</c>.</returns>
+        protected static bool MergeAttribute(IDictionary<string, string> attributes, string key, string value)
+        {
+            if (attributes.ContainsKey(key))
+            {
+                return false;
+            }
+
+            attributes.Add(key, value);
+            return true;
+        }
 
         /// <summary>
         /// Gets the error message formatted using the <see cref="Attribute"/>.

src/Microsoft.AspNetCore.Mvc.DataAnnotations/Internal/ValidationAttributeAdapterProvider.cs

@@ -51,7 +51,7 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
             }
             else if (type == typeof(CreditCardAttribute))
             {
-                adapter = new DataTypeAttributeAdapter((DataTypeAttribute)attribute, "creditcard", stringLocalizer);
+                adapter = new DataTypeAttributeAdapter((DataTypeAttribute)attribute, "data-val-creditcard", stringLocalizer);
             }
             else if (type == typeof(StringLengthAttribute))
             {
@@ -63,15 +63,15 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
             }
             else if (type == typeof(EmailAddressAttribute))
             {
-                adapter = new DataTypeAttributeAdapter((DataTypeAttribute)attribute, "email", stringLocalizer);
+                adapter = new DataTypeAttributeAdapter((DataTypeAttribute)attribute, "data-val-email", stringLocalizer);
             }
             else if (type == typeof(PhoneAttribute))
             {
-                adapter = new DataTypeAttributeAdapter((DataTypeAttribute)attribute, "phone", stringLocalizer);
+                adapter = new DataTypeAttributeAdapter((DataTypeAttribute)attribute, "data-val-phone", stringLocalizer);
             }
             else if (type == typeof(UrlAttribute))
             {
-                adapter = new DataTypeAttributeAdapter((DataTypeAttribute)attribute, "url", stringLocalizer);
+                adapter = new DataTypeAttributeAdapter((DataTypeAttribute)attribute, "data-val-url", stringLocalizer);
             }
             else
             {

src/Microsoft.AspNetCore.Mvc.ViewFeatures/Internal/ModelClientValidationRemoteRule.cs

@@ -1,46 +0,0 @@
-// Copyright (c) .NET Foundation. All rights reserved.
-// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
-
-using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
-
-namespace Microsoft.AspNetCore.Mvc.Internal
-{
-    /// <summary>
-    /// <see cref="ModelClientValidationRule"/> containing information for HTML attribute generation in fields a
-    /// <see cref="RemoteAttribute"/> targets.
-    /// </summary>
-    public class ModelClientValidationRemoteRule : ModelClientValidationRule
-    {
-        private const string RemoteValidationType = "remote";
-        private const string AdditionalFieldsValidationParameter = "additionalfields";
-        private const string TypeValidationParameter = "type";
-        private const string UrlValidationParameter = "url";
-
-        /// <summary>
-        /// Initializes a new instance of the <see cref="ModelClientValidationRemoteRule"/> class.
-        /// </summary>
-        /// <param name="errorMessage">Error message client should display when validation fails.</param>
-        /// <param name="url">URL where client should send a validation request.</param>
-        /// <param name="httpMethod">
-        /// HTTP method (<c>"GET"</c> or <c>"POST"</c>) client should use when sending a validation request.
-        /// </param>
-        /// <param name="additionalFields">
-        /// Comma-separated names of fields the client should include in a validation request.
-        /// </param>
-        public ModelClientValidationRemoteRule(
-            string errorMessage,
-            string url,
-            string httpMethod,
-            string additionalFields)
-            : base(validationType: RemoteValidationType, errorMessage: errorMessage)
-        {
-            ValidationParameters[UrlValidationParameter] = url;
-            if (!string.IsNullOrEmpty(httpMethod))
-            {
-                ValidationParameters[TypeValidationParameter] = httpMethod;
-            }
-
-            ValidationParameters[AdditionalFieldsValidationParameter] = additionalFields;
-        }
-    }
-}

src/Microsoft.AspNetCore.Mvc.ViewFeatures/RemoteAttribute.cs

@@ -232,26 +232,37 @@ namespace Microsoft.AspNetCore.Mvc
             return true;
         }
 
-        /// <inheritdoc />
+        public virtual void AddValidation(ClientModelValidationContext context)
-        /// <exception cref="InvalidOperationException">
-        /// Thrown if unable to generate a target URL for a validation request.
-        /// </exception>
-        public virtual IEnumerable<ModelClientValidationRule> GetClientValidationRules(
-            ClientModelValidationContext context)
         {
             if (context == null)
             {
                 throw new ArgumentNullException(nameof(context));
             }
 
-            var metadata = context.ModelMetadata;
+            MergeAttribute(context.Attributes, "data-val", "true");
-            var rule = new ModelClientValidationRemoteRule(
-                FormatErrorMessage(metadata.GetDisplayName()),
-                GetUrl(context),
-                HttpMethod,
-                FormatAdditionalFieldsForClientValidation(metadata.PropertyName));
 
-            return new[] { rule };
+            var errorMessage = FormatErrorMessage(context.ModelMetadata.GetDisplayName());
+            MergeAttribute(context.Attributes, "data-val-remote", errorMessage);
+            MergeAttribute(context.Attributes, "data-val-remote-url", GetUrl(context));
+
+            if (!string.IsNullOrEmpty(HttpMethod))
+            {
+                MergeAttribute(context.Attributes, "data-val-remote-type", HttpMethod);
+            }
+
+            var additionalFields = FormatAdditionalFieldsForClientValidation(context.ModelMetadata.PropertyName);
+            MergeAttribute(context.Attributes, "data-val-remote-additionalfields", additionalFields);
+        }
+
+        private static bool MergeAttribute(IDictionary<string, string> attributes, string key, string value)
+        {
+            if (attributes.ContainsKey(key))
+            {
+                return false;
+            }
+
+            attributes.Add(key, value);
+            return true;
         }
 
         private static IEnumerable<string> SplitAndTrimPropertyNames(string original)

src/Microsoft.AspNetCore.Mvc.ViewFeatures/Rendering/IHtmlHelper.cs

@@ -7,7 +7,6 @@ using System.Text.Encodings.Web;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Html;
 using Microsoft.AspNetCore.Mvc.ModelBinding;
-using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
 using Microsoft.AspNetCore.Mvc.ViewFeatures;
 
 namespace Microsoft.AspNetCore.Mvc.Rendering
@@ -375,20 +374,6 @@ namespace Microsoft.AspNetCore.Mvc.Rendering
         /// <returns>A <see cref="string"/> containing the element Id.</returns>
         string GenerateIdFromName(string fullName);
 
-        /// <summary>
-        /// Returns information about about client validation rules for the specified <paramref name="metadata"/> or
-        /// <paramref name="expression"/>. Intended for use in <see cref="IHtmlHelper"/> extension methods.
-        /// </summary>
-        /// <param name="metadata">Metadata about the <see cref="object"/> of interest.</param>
-        /// <param name="expression">
-        /// Expression name, relative to the current model. Used to determine <see cref="ModelMetadata"/> when
-        /// <paramref name="metadata"/> is <c>null</c>; ignored otherwise.
-        /// </param>
-        /// <returns>An <see cref="IEnumerable{ModelClientValidationRule}"/> containing the relevant rules.</returns>
-        IEnumerable<ModelClientValidationRule> GetClientValidationRules(
-            ModelExplorer modelExplorer,
-            string expression);
-
         /// <summary>
         /// Returns a select list for the given <typeparamref name="TEnum"/>.
         /// </summary>

src/Microsoft.AspNetCore.Mvc.ViewFeatures/ViewFeatures/DefaultHtmlGenerator.cs

@@ -569,7 +569,7 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
                 }
             }
 
-            tagBuilder.MergeAttributes(GetValidationAttributes(viewContext, modelExplorer, expression));
+            AddValidationAttributes(viewContext, tagBuilder, modelExplorer, expression);
 
             return tagBuilder;
         }
@@ -640,7 +640,7 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
             }
 
             tagBuilder.MergeAttribute("name", fullName, true);
-            tagBuilder.MergeAttributes(GetValidationAttributes(viewContext, modelExplorer, expression));
+            AddValidationAttributes(viewContext, tagBuilder, modelExplorer, expression);
 
             // If there are any errors for a named field, we add this CSS attribute.
             if (entry != null && entry.Errors.Count > 0)
@@ -865,31 +865,6 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
             return tagBuilder;
         }
 
-        /// <inheritdoc />
-        public IEnumerable<ModelClientValidationRule> GetClientValidationRules(
-            ViewContext viewContext,
-            ModelExplorer modelExplorer,
-            string expression)
-        {
-            if (viewContext == null)
-            {
-                throw new ArgumentNullException(nameof(viewContext));
-            }
-
-            modelExplorer = modelExplorer ??
-                ExpressionMetadataProvider.FromStringExpression(expression, viewContext.ViewData, _metadataProvider);
-            var validationContext = new ClientModelValidationContext(
-                viewContext,
-                modelExplorer.Metadata,
-                _metadataProvider);
-
-            var validatorProviderContext = new ClientValidatorProviderContext(modelExplorer.Metadata);
-            _clientModelValidatorProvider.GetValidators(validatorProviderContext);
-
-            var validators = validatorProviderContext.Validators;
-            return validators.SelectMany(v => v.GetClientValidationRules(validationContext));
-        }
-
         /// <inheritdoc />
         public virtual ICollection<string> GetCurrentValues(
             ViewContext viewContext,
@@ -1251,7 +1226,7 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
                 tagBuilder.AddCssClass(HtmlHelper.ValidationInputCssClassName);
             }
 
-            tagBuilder.MergeAttributes(GetValidationAttributes(viewContext, modelExplorer, expression));
+            AddValidationAttributes(viewContext, tagBuilder, modelExplorer, expression);
 
             return tagBuilder;
         }
@@ -1275,30 +1250,58 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
             return tagBuilder;
         }
 
-        // Only render attributes if client-side validation is enabled, and then only if we've
+        /// <summary>
-        // never rendered validation for a field with this name in this form.
+        /// Adds validation attributes to the <paramref name="tagBuilder" /> if client validation
-        protected virtual IDictionary<string, object> GetValidationAttributes(
+        /// is enabled.
+        /// </summary>
+        /// <param name="viewContext">A <see cref="ViewContext"/> instance for the current scope.</param>
+        /// <param name="tagBuilder">A <see cref="TagBuilder"/> instance.</param>
+        /// <param name="modelExplorer">The <see cref="ModelExplorer"/> for the <paramref name="expression"/>.</param>
+        /// <param name="expression">Expression name, relative to the current model.</param>
+        protected virtual void AddValidationAttributes(
             ViewContext viewContext,
+            TagBuilder tagBuilder,
             ModelExplorer modelExplorer,
             string expression)
         {
+            // Only render attributes if client-side validation is enabled, and then only if we've
+            // never rendered validation for a field with this name in this form.
             var formContext = viewContext.ClientValidationEnabled ? viewContext.FormContext : null;
             if (formContext == null)
             {
-                return null;
+                return;
             }
 
             var fullName = GetFullHtmlFieldName(viewContext, expression);
             if (formContext.RenderedField(fullName))
             {
-                return null;
+                return;
             }
 
             formContext.RenderedField(fullName, true);
 
-            var clientRules = GetClientValidationRules(viewContext, modelExplorer, expression);
+            modelExplorer = modelExplorer ??
+                ExpressionMetadataProvider.FromStringExpression(expression, viewContext.ViewData, _metadataProvider);
 
-            return UnobtrusiveValidationAttributesGenerator.GetValidationAttributes(clientRules);
+
+            var validatorProviderContext = new ClientValidatorProviderContext(modelExplorer.Metadata);
+            _clientModelValidatorProvider.GetValidators(validatorProviderContext);
+
+            var validators = validatorProviderContext.Validators;
+            if (validators.Count > 0)
+            {
+                var validationContext = new ClientModelValidationContext(
+                    viewContext,
+                    modelExplorer.Metadata,
+                    _metadataProvider,
+                    tagBuilder.Attributes);
+
+                for (var i = 0; i < validators.Count; i++)
+                {
+                    var validator = validators[i];
+                    validator.AddValidation(validationContext);
+                }
+            }
         }
 
         private static Enum ConvertEnumFromInteger(object value, Type targetType)

src/Microsoft.AspNetCore.Mvc.ViewFeatures/ViewFeatures/HtmlHelper.cs

@@ -1212,14 +1212,6 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
             return resolvedValue;
         }
 
-        /// <inheritdoc />
-        public IEnumerable<ModelClientValidationRule> GetClientValidationRules(
-            ModelExplorer modelExplorer,
-            string expression)
-        {
-            return _htmlGenerator.GetClientValidationRules(ViewContext, modelExplorer, expression);
-        }
-
         /// <summary>
         /// Returns a select list for the given <paramref name="metadata"/>.
         /// </summary>

src/Microsoft.AspNetCore.Mvc.ViewFeatures/ViewFeatures/IHtmlGenerator.cs

@@ -365,15 +365,6 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
             string headerTag,
             object htmlAttributes);
 
-        /// <remarks>
-        /// Not used directly in <see cref="HtmlHelper"/>. Exposed publicly for use in other <see cref="IHtmlHelper"/>
-        /// implementations.
-        /// </remarks>
-        IEnumerable<ModelClientValidationRule> GetClientValidationRules(
-            ViewContext viewContext,
-            ModelExplorer modelExplorer,
-            string expression);
-
         /// <summary>
         /// Gets the collection of current values for the given <paramref name="expression"/>.
         /// </summary>

src/Microsoft.AspNetCore.Mvc.ViewFeatures/ViewFeatures/UnobtrusiveValidationAttributesGenerator.cs

@@ -1,96 +0,0 @@
-// Copyright (c) .NET Foundation. All rights reserved.
-// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
-
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
-
-namespace Microsoft.AspNetCore.Mvc.ViewFeatures
-{
-    public static class UnobtrusiveValidationAttributesGenerator
-    {
-        public static IDictionary<string, object> GetValidationAttributes(
-            IEnumerable<ModelClientValidationRule> clientRules)
-        {
-            if (clientRules == null)
-            {
-                throw new ArgumentNullException(nameof(clientRules));
-            }
-
-            IDictionary<string, object> results = null;
-
-            foreach (var rule in clientRules)
-            {
-                if (results == null)
-                {
-                    results = new Dictionary<string, object>(StringComparer.Ordinal);
-                }
-
-                var ruleName = "data-val-" + rule.ValidationType;
-
-                ValidateUnobtrusiveValidationRule(rule, results, ruleName);
-
-                results.Add(ruleName, rule.ErrorMessage ?? string.Empty);
-                ruleName += "-";
-
-                foreach (var kvp in rule.ValidationParameters)
-                {
-                    results.Add(ruleName + kvp.Key, kvp.Value ?? string.Empty);
-                }
-            }
-
-            if (results != null)
-            {
-                results.Add("data-val", "true");
-            }
-
-            return results;
-        }
-
-        private static void ValidateUnobtrusiveValidationRule(
-            ModelClientValidationRule rule,
-            IDictionary<string, object> resultsDictionary,
-            string dictionaryKey)
-        {
-            if (string.IsNullOrEmpty(rule.ValidationType))
-            {
-                throw new ArgumentException(
-                    Resources.FormatUnobtrusiveJavascript_ValidationTypeCannotBeEmpty(rule.GetType().FullName),
-                    nameof(rule));
-            }
-
-            if (resultsDictionary.ContainsKey(dictionaryKey))
-            {
-                throw new InvalidOperationException(
-                    Resources.FormatUnobtrusiveJavascript_ValidationTypeMustBeUnique(rule.ValidationType));
-            }
-
-            if (!rule.ValidationType.All(char.IsLower))
-            {
-                throw new InvalidOperationException(
-                    Resources.FormatUnobtrusiveJavascript_ValidationTypeMustBeLegal(
-                        rule.ValidationType,
-                        rule.GetType().FullName));
-            }
-
-            foreach (var key in rule.ValidationParameters.Keys)
-            {
-                if (string.IsNullOrEmpty(key))
-                {
-                    throw new InvalidOperationException(
-                        Resources.FormatUnobtrusiveJavascript_ValidationParameterCannotBeEmpty(
-                            rule.GetType().FullName));
-                }
-
-                if (!char.IsLower(key[0]) || key.Any(c => !char.IsLower(c) && !char.IsDigit(c)))
-                {
-                    throw new InvalidOperationException(
-                        Resources.FormatUnobtrusiveJavascript_ValidationParameterMustBeLegal(
-                            key,
-                            rule.GetType().FullName));
-                }
-            }
-        }
-    }
-}

test/Microsoft.AspNetCore.Mvc.Core.Test/ModelBinding/Metadata/DefaultValidationMetadataProviderTest.cs

@@ -79,7 +79,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Metadata
 
         private class TestClientModelValidationAttribute : Attribute, IClientModelValidator
         {
-            public IEnumerable<ModelClientValidationRule> GetClientValidationRules(ClientModelValidationContext context)
+            public void AddValidation(ClientModelValidationContext context)
             {
                 throw new NotImplementedException();
             }
@@ -87,7 +87,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Metadata
 
         private class TestValidationAttribute : Attribute, IModelValidator, IClientModelValidator
         {
-            public IEnumerable<ModelClientValidationRule> GetClientValidationRules(ClientModelValidationContext context)
+            public void AddValidation(ClientModelValidationContext context)
             {
                 throw new NotImplementedException();
             }

test/Microsoft.AspNetCore.Mvc.DataAnnotations.Test/Internal/CompareAttributeAdapterTest.cs

@@ -4,6 +4,7 @@
 using System.ComponentModel.DataAnnotations;
 using Microsoft.AspNetCore.Mvc.ModelBinding;
 using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
+using Microsoft.AspNetCore.Mvc.ViewFeatures;
 using Microsoft.AspNetCore.Testing;
 using Microsoft.AspNetCore.Testing.xunit;
 using Microsoft.Extensions.Localization;
@@ -25,19 +26,30 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
             var attribute = new CompareAttribute("OtherProperty");
             var adapter = new CompareAttributeAdapter(attribute, stringLocalizer: null);
 
+            // Mono issue - https://github.com/aspnet/External/issues/19
+            var expectedMessage = PlatformNormalizer.NormalizeContent(
+                    "'MyPropertyDisplayName' and 'OtherPropertyDisplayName' do not match.");
+
             var actionContext = new ActionContext();
-            var context = new ClientModelValidationContext(actionContext, metadata, metadataProvider);
+            var context = new ClientModelValidationContext(
+                actionContext,
+                metadata,
+                metadataProvider,
+                new AttributeDictionary());
 
             // Act
-            var rules = adapter.GetClientValidationRules(context);
+            adapter.AddValidation(context);
 
             // Assert
-            var rule = Assert.Single(rules);
+            Assert.Collection(
-            // Mono issue - https://github.com/aspnet/External/issues/19
+                context.Attributes,
-            Assert.Equal(
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
-                PlatformNormalizer.NormalizeContent(
+                kvp => { Assert.Equal("data-val-equalto", kvp.Key); Assert.Equal(expectedMessage, kvp.Value); },
-                    "'MyPropertyDisplayName' and 'OtherPropertyDisplayName' do not match."),
+                kvp =>
-                rule.ErrorMessage);
+                {
+                    Assert.Equal("data-val-equalto-other", kvp.Key);
+                    Assert.Equal(kvp.Value, "*.OtherProperty");
+                });
         }
 
         [Fact]
@@ -62,15 +74,25 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
             var adapter = new CompareAttributeAdapter(attribute, stringLocalizer: stringLocalizer.Object);
 
             var actionContext = new ActionContext();
-            var context = new ClientModelValidationContext(actionContext, metadata, metadataProvider);
+            var context = new ClientModelValidationContext(
+                actionContext,
+                metadata,
+                metadataProvider,
+                new AttributeDictionary());
 
             // Act
-            var rules = adapter.GetClientValidationRules(context);
+            adapter.AddValidation(context);
 
             // Assert
-            var rule = Assert.Single(rules);
+            Assert.Collection(
-            // Mono issue - https://github.com/aspnet/External/issues/19
+                context.Attributes,
-            Assert.Equal(expectedMessage, rule.ErrorMessage);
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
+                kvp => { Assert.Equal("data-val-equalto", kvp.Key); Assert.Equal(expectedMessage, kvp.Value); },
+                kvp =>
+                {
+                    Assert.Equal("data-val-equalto-other", kvp.Key);
+                    Assert.Equal(kvp.Value, "*.OtherProperty");
+                });
         }
 
         [Fact]
@@ -84,18 +106,29 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
             var attribute = new CompareAttribute("OtherProperty");
             var adapter = new CompareAttributeAdapter(attribute, stringLocalizer: null);
 
+            // Mono issue - https://github.com/aspnet/External/issues/19
+            var expectedMessage = PlatformNormalizer.NormalizeContent("'MyProperty' and 'OtherProperty' do not match.");
+
             var actionContext = new ActionContext();
-            var context = new ClientModelValidationContext(actionContext, metadata, metadataProvider);
+            var context = new ClientModelValidationContext(
+                actionContext,
+                metadata,
+                metadataProvider,
+                new AttributeDictionary());
 
             // Act
-            var rules = adapter.GetClientValidationRules(context);
+            adapter.AddValidation(context);
 
             // Assert
-            var rule = Assert.Single(rules);
+            Assert.Collection(
-            // Mono issue - https://github.com/aspnet/External/issues/19
+                context.Attributes,
-            Assert.Equal(
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
-                PlatformNormalizer.NormalizeContent("'MyProperty' and 'OtherProperty' do not match."),
+                kvp => { Assert.Equal("data-val-equalto", kvp.Key); Assert.Equal(expectedMessage, kvp.Value); },
-                rule.ErrorMessage);
+                kvp =>
+                {
+                    Assert.Equal("data-val-equalto-other", kvp.Key);
+                    Assert.Equal(kvp.Value, "*.OtherProperty");
+                });
         }
 
         [Fact]
@@ -111,15 +144,28 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
             };
             var adapter = new CompareAttributeAdapter(attribute, stringLocalizer: null);
 
+            var expectedMessage = "Hello 'MyProperty', goodbye 'OtherProperty'.";
+
             var actionContext = new ActionContext();
-            var context = new ClientModelValidationContext(actionContext, metadata, metadataProvider);
+            var context = new ClientModelValidationContext(
+                actionContext,
+                metadata,
+                metadataProvider,
+                new AttributeDictionary());
 
             // Act
-            var rules = adapter.GetClientValidationRules(context);
+            adapter.AddValidation(context);
 
             // Assert
-            var rule = Assert.Single(rules);
+            Assert.Collection(
-            Assert.Equal("Hello 'MyProperty', goodbye 'OtherProperty'.", rule.ErrorMessage);
+                context.Attributes,
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
+                kvp => { Assert.Equal("data-val-equalto", kvp.Key); Assert.Equal(expectedMessage, kvp.Value); },
+                kvp =>
+                {
+                    Assert.Equal("data-val-equalto-other", kvp.Key);
+                    Assert.Equal(kvp.Value, "*.OtherProperty");
+                });
         }
 
         [ConditionalFact]
@@ -138,15 +184,61 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
             };
             var adapter = new CompareAttributeAdapter(attribute, stringLocalizer: null);
 
+            var expectedMessage = "Comparing MyProperty to OtherProperty.";
+
             var actionContext = new ActionContext();
-            var context = new ClientModelValidationContext(actionContext, metadata, metadataProvider);
+            var context = new ClientModelValidationContext(
+                actionContext,
+                metadata,
+                metadataProvider,
+                new AttributeDictionary());
 
             // Act
-            var rules = adapter.GetClientValidationRules(context);
+            adapter.AddValidation(context);
 
             // Assert
-            var rule = Assert.Single(rules);
+            Assert.Collection(
-            Assert.Equal("Comparing MyProperty to OtherProperty.", rule.ErrorMessage);
+                context.Attributes,
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
+                kvp => { Assert.Equal("data-val-equalto", kvp.Key); Assert.Equal(expectedMessage, kvp.Value); },
+                kvp =>
+                {
+                    Assert.Equal("data-val-equalto-other", kvp.Key);
+                    Assert.Equal(kvp.Value, "*.OtherProperty");
+                });
+        }
+
+        [Fact]
+        [ReplaceCulture]
+        public void AddValidation_DoesNotTrounceExistingAttributes()
+        {
+            // Arrange
+            var metadataProvider = TestModelMetadataProvider.CreateDefaultProvider();
+            var metadata = metadataProvider.GetMetadataForProperty(typeof(PropertyNameModel), "MyProperty");
+
+            var attribute = new CompareAttribute("OtherProperty");
+            var adapter = new CompareAttributeAdapter(attribute, stringLocalizer: null);
+
+            var actionContext = new ActionContext();
+            var context = new ClientModelValidationContext(
+                actionContext,
+                metadata,
+                metadataProvider,
+                new AttributeDictionary());
+
+            context.Attributes.Add("data-val", "original");
+            context.Attributes.Add("data-val-equalto", "original");
+            context.Attributes.Add("data-val-equalto-other", "original");
+
+            // Act
+            adapter.AddValidation(context);
+
+            // Assert
+            Assert.Collection(
+                context.Attributes,
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("original", kvp.Value); },
+                kvp => { Assert.Equal("data-val-equalto", kvp.Key); Assert.Equal("original", kvp.Value); },
+                kvp => { Assert.Equal("data-val-equalto-other", kvp.Key); Assert.Equal("original", kvp.Value); });
         }
 
         private class PropertyDisplayNameModel

test/Microsoft.AspNetCore.Mvc.DataAnnotations.Test/Internal/DataAnnotationsMetadataProviderTest.cs

@@ -672,7 +672,7 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
 
         private class TestValidationAttribute : ValidationAttribute, IClientModelValidator
         {
-            public IEnumerable<ModelClientValidationRule> GetClientValidationRules(ClientModelValidationContext context)
+            public void AddValidation(ClientModelValidationContext context)
             {
                 throw new NotImplementedException();
             }

test/Microsoft.AspNetCore.Mvc.DataAnnotations.Test/Internal/DefaultModelClientValidatorProviderTest.cs

@@ -245,9 +245,8 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
 
         private class CustomValidationAttribute : Attribute, IClientModelValidator
         {
-            public IEnumerable<ModelClientValidationRule> GetClientValidationRules(ClientModelValidationContext context)
+            public void AddValidation(ClientModelValidationContext context)
             {
-                return Enumerable.Empty<ModelClientValidationRule>();
             }
         }
 

test/Microsoft.AspNetCore.Mvc.DataAnnotations.Test/Internal/MaxLengthAttributeAdapterTest.cs

@@ -4,6 +4,7 @@
 using System.ComponentModel.DataAnnotations;
 using Microsoft.AspNetCore.Mvc.ModelBinding;
 using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
+using Microsoft.AspNetCore.Mvc.ViewFeatures;
 using Microsoft.AspNetCore.Testing;
 using Microsoft.Extensions.Localization;
 using Moq;
@@ -15,7 +16,7 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
     {
         [Fact]
         [ReplaceCulture]
-        public void ClientRulesWithMaxLengthAttribute_Localize()
+        public void MaxLengthAttribute_AddValidation_Localize()
         {
             // Arrange
             var provider = TestModelMetadataProvider.CreateDefaultProvider();
@@ -34,22 +35,22 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
             var adapter = new MaxLengthAttributeAdapter(attribute, stringLocalizer: stringLocalizer.Object);
 
             var actionContext = new ActionContext();
-            var context = new ClientModelValidationContext(actionContext, metadata, provider);
+            var context = new ClientModelValidationContext(actionContext, metadata, provider, new AttributeDictionary());
 
             // Act
-            var rules = adapter.GetClientValidationRules(context);
+            adapter.AddValidation(context);
 
             // Assert
-            var rule = Assert.Single(rules);
+            Assert.Collection(
-            Assert.Equal("maxlength", rule.ValidationType);
+                context.Attributes,
-            Assert.Equal(1, rule.ValidationParameters.Count);
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
-            Assert.Equal(10, rule.ValidationParameters["max"]);
+                kvp => { Assert.Equal("data-val-maxlength", kvp.Key); Assert.Equal(expectedMessage, kvp.Value); },
-            Assert.Equal(attribute.FormatErrorMessage("Length"), rule.ErrorMessage);
+                kvp => { Assert.Equal("data-val-maxlength-max", kvp.Key); Assert.Equal("10", kvp.Value); });
         }
 
         [Fact]
         [ReplaceCulture]
-        public void ClientRulesWithMaxLengthAttribute()
+        public void MaxLengthAttribute_AddValidation()
         {
             // Arrange
             var provider = TestModelMetadataProvider.CreateDefaultProvider();
@@ -58,23 +59,25 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
             var attribute = new MaxLengthAttribute(10);
             var adapter = new MaxLengthAttributeAdapter(attribute, stringLocalizer: null);
 
+            var expectedMessage = attribute.FormatErrorMessage("Length");
+
             var actionContext = new ActionContext();
-            var context = new ClientModelValidationContext(actionContext, metadata, provider);
+            var context = new ClientModelValidationContext(actionContext, metadata, provider, new AttributeDictionary());
 
             // Act
-            var rules = adapter.GetClientValidationRules(context);
+            adapter.AddValidation(context);
 
             // Assert
-            var rule = Assert.Single(rules);
+            Assert.Collection(
-            Assert.Equal("maxlength", rule.ValidationType);
+                context.Attributes,
-            Assert.Equal(1, rule.ValidationParameters.Count);
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
-            Assert.Equal(10, rule.ValidationParameters["max"]);
+                kvp => { Assert.Equal("data-val-maxlength", kvp.Key); Assert.Equal(expectedMessage, kvp.Value); },
-            Assert.Equal(attribute.FormatErrorMessage("Length"), rule.ErrorMessage);
+                kvp => { Assert.Equal("data-val-maxlength-max", kvp.Key); Assert.Equal("10", kvp.Value); });
         }
 
         [Fact]
         [ReplaceCulture]
-        public void ClientRulesWithMaxLengthAttributeAndCustomMessage()
+        public void MaxLengthAttribute_AddValidation_CustomMessage()
         {
             // Arrange
             var propertyName = "Length";
@@ -82,26 +85,28 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
             var provider = TestModelMetadataProvider.CreateDefaultProvider();
             var metadata = provider.GetMetadataForProperty(typeof(string), propertyName);
 
+            var expectedMessage = "Length must be at most 5";
+
             var attribute = new MaxLengthAttribute(5) { ErrorMessage = message };
             var adapter = new MaxLengthAttributeAdapter(attribute, stringLocalizer: null);
 
             var actionContext = new ActionContext();
-            var context = new ClientModelValidationContext(actionContext, metadata, provider);
+            var context = new ClientModelValidationContext(actionContext, metadata, provider, new AttributeDictionary());
 
             // Act
-            var rules = adapter.GetClientValidationRules(context);
+            adapter.AddValidation(context);
 
             // Assert
-            var rule = Assert.Single(rules);
+            Assert.Collection(
-            Assert.Equal("maxlength", rule.ValidationType);
+                context.Attributes,
-            Assert.Equal(1, rule.ValidationParameters.Count);
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
-            Assert.Equal(5, rule.ValidationParameters["max"]);
+                kvp => { Assert.Equal("data-val-maxlength", kvp.Key); Assert.Equal(expectedMessage, kvp.Value); },
-            Assert.Equal("Length must be at most 5", rule.ErrorMessage);
+                kvp => { Assert.Equal("data-val-maxlength-max", kvp.Key); Assert.Equal("5", kvp.Value); });
         }
 
         [Fact]
         [ReplaceCulture]
-        public void ClientRulesWithMaxLengthAttribute_StringLocalizer_ReturnsLocalizedErrorString()
+        public void MaxLengthAttribute_AddValidation_StringLocalizer_ReturnsLocalizedErrorString()
         {
             // Arrange
             var provider = TestModelMetadataProvider.CreateDefaultProvider();
@@ -114,20 +119,53 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
             var stringLocalizer = new Mock<IStringLocalizer>();
             stringLocalizer.Setup(s => s[errorKey, metadata.GetDisplayName(), attribute.Length]).Returns(localizedString);
 
+            var expectedMessage = "Longueur est invalide";
+
             var adapter = new MaxLengthAttributeAdapter(attribute, stringLocalizer.Object);
 
             var actionContext = new ActionContext();
-            var context = new ClientModelValidationContext(actionContext, metadata, provider);
+            var context = new ClientModelValidationContext(actionContext, metadata, provider, new AttributeDictionary());
 
             // Act
-            var rules = adapter.GetClientValidationRules(context);
+            adapter.AddValidation(context);
 
             // Assert
-            var rule = Assert.Single(rules);
+            Assert.Collection(
-            Assert.Equal("maxlength", rule.ValidationType);
+                context.Attributes,
-            Assert.Equal(1, rule.ValidationParameters.Count);
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
-            Assert.Equal(10, rule.ValidationParameters["max"]);
+                kvp => { Assert.Equal("data-val-maxlength", kvp.Key); Assert.Equal(expectedMessage, kvp.Value); },
-            Assert.Equal("Longueur est invalide", rule.ErrorMessage);
+                kvp => { Assert.Equal("data-val-maxlength-max", kvp.Key); Assert.Equal("10", kvp.Value); });
+        }
+
+        [Fact]
+        [ReplaceCulture]
+        public void AddValidation_DoesNotTrounceExistingAttributes()
+        {
+            // Arrange
+            var provider = TestModelMetadataProvider.CreateDefaultProvider();
+            var metadata = provider.GetMetadataForProperty(typeof(string), "Length");
+
+            var attribute = new MaxLengthAttribute(10);
+            var adapter = new MaxLengthAttributeAdapter(attribute, stringLocalizer: null);
+
+            var expectedMessage = attribute.FormatErrorMessage("Length");
+
+            var actionContext = new ActionContext();
+            var context = new ClientModelValidationContext(actionContext, metadata, provider, new AttributeDictionary());
+
+            context.Attributes.Add("data-val", "original");
+            context.Attributes.Add("data-val-maxlength", "original");
+            context.Attributes.Add("data-val-maxlength-max", "original");
+
+            // Act
+            adapter.AddValidation(context);
+
+            // Assert
+            Assert.Collection(
+                context.Attributes,
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("original", kvp.Value); },
+                kvp => { Assert.Equal("data-val-maxlength", kvp.Key); Assert.Equal("original", kvp.Value); },
+                kvp => { Assert.Equal("data-val-maxlength-max", kvp.Key); Assert.Equal("original", kvp.Value); });
         }
     }
 }

test/Microsoft.AspNetCore.Mvc.DataAnnotations.Test/Internal/MinLengthAttributeAdapterTest.cs

@@ -4,6 +4,7 @@
 using System.ComponentModel.DataAnnotations;
 using Microsoft.AspNetCore.Mvc.ModelBinding;
 using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
+using Microsoft.AspNetCore.Mvc.ViewFeatures;
 using Microsoft.AspNetCore.Testing;
 using Microsoft.Extensions.Localization;
 using Moq;
@@ -15,7 +16,7 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
     {
         [Fact]
         [ReplaceCulture]
-        public void ClientRulesWithMinLengthAttribute_Localize()
+        public void MinLengthAttribute_AddValidation_Localize()
         {
             // Arrange
             var provider = TestModelMetadataProvider.CreateDefaultProvider();
@@ -34,22 +35,22 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
             var adapter = new MinLengthAttributeAdapter(attribute, stringLocalizer: stringLocalizer.Object);
 
             var actionContext = new ActionContext();
-            var context = new ClientModelValidationContext(actionContext, metadata, provider);
+            var context = new ClientModelValidationContext(actionContext, metadata, provider, new AttributeDictionary());
 
             // Act
-            var rules = adapter.GetClientValidationRules(context);
+            adapter.AddValidation(context);
 
             // Assert
-            var rule = Assert.Single(rules);
+            Assert.Collection(
-            Assert.Equal("minlength", rule.ValidationType);
+                context.Attributes,
-            Assert.Equal(1, rule.ValidationParameters.Count);
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
-            Assert.Equal(6, rule.ValidationParameters["min"]);
+                kvp => { Assert.Equal("data-val-minlength", kvp.Key); Assert.Equal(expectedMessage, kvp.Value); },
-            Assert.Equal(attribute.FormatErrorMessage("Length"), rule.ErrorMessage);
+                kvp => { Assert.Equal("data-val-minlength-min", kvp.Key); Assert.Equal("6", kvp.Value); });
         }
 
         [Fact]
         [ReplaceCulture]
-        public void ClientRulesWithMinLengthAttribute()
+        public void MinLengthAttribute_AddValidation_Attribute()
         {
             // Arrange
             var provider = TestModelMetadataProvider.CreateDefaultProvider();
@@ -58,45 +59,78 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
             var attribute = new MinLengthAttribute(6);
             var adapter = new MinLengthAttributeAdapter(attribute, stringLocalizer: null);
 
+            var expectedMessage = attribute.FormatErrorMessage("Length");
+
             var actionContext = new ActionContext();
-            var context = new ClientModelValidationContext(actionContext, metadata, provider);
+            var context = new ClientModelValidationContext(actionContext, metadata, provider, new AttributeDictionary());
 
             // Act
-            var rules = adapter.GetClientValidationRules(context);
+            adapter.AddValidation(context);
 
             // Assert
-            var rule = Assert.Single(rules);
+            Assert.Collection(
-            Assert.Equal("minlength", rule.ValidationType);
+                context.Attributes,
-            Assert.Equal(1, rule.ValidationParameters.Count);
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
-            Assert.Equal(6, rule.ValidationParameters["min"]);
+                kvp => { Assert.Equal("data-val-minlength", kvp.Key); Assert.Equal(expectedMessage, kvp.Value); },
-            Assert.Equal(attribute.FormatErrorMessage("Length"), rule.ErrorMessage);
+                kvp => { Assert.Equal("data-val-minlength-min", kvp.Key); Assert.Equal("6", kvp.Value); });
         }
 
         [Fact]
         [ReplaceCulture]
-        public void ClientRulesWithMinLengthAttributeAndCustomMessage()
+        public void MinLengthAttribute_AddValidation_AttributeAndCustomMessage()
         {
             // Arrange
             var propertyName = "Length";
-            var message = "Array must have at least {1} items.";
             var provider = TestModelMetadataProvider.CreateDefaultProvider();
             var metadata = provider.GetMetadataForProperty(typeof(string), propertyName);
 
-            var attribute = new MinLengthAttribute(2) { ErrorMessage = message };
+            var attribute = new MinLengthAttribute(2) { ErrorMessage = "Array must have at least {1} items." };
+            var adapter = new MinLengthAttributeAdapter(attribute, stringLocalizer: null);
+
+            var expectedMessage = "Array must have at least 2 items.";
+
+            var actionContext = new ActionContext();
+            var context = new ClientModelValidationContext(actionContext, metadata, provider, new AttributeDictionary());
+
+            // Act
+            adapter.AddValidation(context);
+
+            // Assert
+            Assert.Collection(
+                context.Attributes,
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
+                kvp => { Assert.Equal("data-val-minlength", kvp.Key); Assert.Equal(expectedMessage, kvp.Value); },
+                kvp => { Assert.Equal("data-val-minlength-min", kvp.Key); Assert.Equal("2", kvp.Value); });
+        }
+
+        [Fact]
+        [ReplaceCulture]
+        public void AddValidation_DoesNotTrounceExistingAttributes()
+        {
+            // Arrange
+            var propertyName = "Length";
+            var provider = TestModelMetadataProvider.CreateDefaultProvider();
+            var metadata = provider.GetMetadataForProperty(typeof(string), propertyName);
+
+            var attribute = new MinLengthAttribute(2) { ErrorMessage = "Array must have at least {1} items." };
             var adapter = new MinLengthAttributeAdapter(attribute, stringLocalizer: null);
 
             var actionContext = new ActionContext();
-            var context = new ClientModelValidationContext(actionContext, metadata, provider);
+            var context = new ClientModelValidationContext(actionContext, metadata, provider, new AttributeDictionary());
+
+            context.Attributes.Add("data-val", "original");
+            context.Attributes.Add("data-val-minlength", "original");
+            context.Attributes.Add("data-val-minlength-min", "original");
 
             // Act
-            var rules = adapter.GetClientValidationRules(context);
+            adapter.AddValidation(context);
 
             // Assert
-            var rule = Assert.Single(rules);
+            Assert.Collection(
-            Assert.Equal("minlength", rule.ValidationType);
+                context.Attributes,
-            Assert.Equal(1, rule.ValidationParameters.Count);
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("original", kvp.Value); },
-            Assert.Equal(2, rule.ValidationParameters["min"]);
+                kvp => { Assert.Equal("data-val-minlength", kvp.Key); Assert.Equal("original", kvp.Value); },
-            Assert.Equal("Array must have at least 2 items.", rule.ErrorMessage);
+                kvp => { Assert.Equal("data-val-minlength-min", kvp.Key); Assert.Equal("original", kvp.Value); });
         }
     }
 }

test/Microsoft.AspNetCore.Mvc.DataAnnotations.Test/Internal/NumericClientModelValidatorTest.cs

@@ -4,6 +4,7 @@
 using System.ComponentModel.DataAnnotations;
 using Microsoft.AspNetCore.Mvc.ModelBinding;
 using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
+using Microsoft.AspNetCore.Mvc.ViewFeatures;
 using Microsoft.AspNetCore.Testing;
 using Xunit;
 
@@ -13,7 +14,7 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
     {
         [Fact]
         [ReplaceCulture]
-        public void ClientRulesWithCorrectValidationTypeAndErrorMessage()
+        public void AddValidation_CorrectValidationTypeAndErrorMessage()
         {
             // Arrange
             var provider = TestModelMetadataProvider.CreateDefaultProvider();
@@ -22,17 +23,44 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
             var adapter = new NumericClientModelValidator();
 
             var actionContext = new ActionContext();
-            var context = new ClientModelValidationContext(actionContext, metadata, provider);
+            var context = new ClientModelValidationContext(actionContext, metadata, provider, new AttributeDictionary());
 
             var expectedMessage = "The field DisplayId must be a number.";
 
             // Act
-            var rules = adapter.GetClientValidationRules(context);
+            adapter.AddValidation(context);
 
             // Assert
-            var rule = Assert.Single(rules);
+            Assert.Collection(
-            Assert.Equal("number", rule.ValidationType);
+                context.Attributes,
-            Assert.Equal(expectedMessage, rule.ErrorMessage);
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
+                kvp => { Assert.Equal("data-val-number", kvp.Key); Assert.Equal(expectedMessage, kvp.Value); });
+        }
+
+        [Fact]
+        [ReplaceCulture]
+        public void AddValidation_DoesNotTrounceExistingAttributes()
+        {
+            // Arrange
+            var provider = TestModelMetadataProvider.CreateDefaultProvider();
+            var metadata = provider.GetMetadataForProperty(typeof(TypeWithNumericProperty), "Id");
+
+            var adapter = new NumericClientModelValidator();
+
+            var actionContext = new ActionContext();
+            var context = new ClientModelValidationContext(actionContext, metadata, provider, new AttributeDictionary());
+
+            context.Attributes.Add("data-val", "original");
+            context.Attributes.Add("data-val-number", "original");
+
+            // Act
+            adapter.AddValidation(context);
+
+            // Assert
+            Assert.Collection(
+                context.Attributes,
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("original", kvp.Value); },
+                kvp => { Assert.Equal("data-val-number", kvp.Key); Assert.Equal("original", kvp.Value); });
         }
 
         private class TypeWithNumericProperty

test/Microsoft.AspNetCore.Mvc.DataAnnotations.Test/Internal/RangeAttributeAdapterTest.cs

@@ -3,6 +3,7 @@
 
 using System.ComponentModel.DataAnnotations;
 using Microsoft.AspNetCore.Mvc.DataAnnotations.Internal;
+using Microsoft.AspNetCore.Mvc.ViewFeatures;
 using Microsoft.AspNetCore.Testing;
 using Microsoft.Extensions.Localization;
 using Moq;
@@ -14,7 +15,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Validation
     {
         [Fact]
         [ReplaceCulture]
-        public void GetClientValidationRules_ReturnsValidationParameters_WithoutLocalization()
+        public void AddValidation_WithoutLocalization()
         {
             // Arrange
             var provider = TestModelMetadataProvider.CreateDefaultProvider();
@@ -28,23 +29,23 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Validation
             var adapter = new RangeAttributeAdapter(attribute, stringLocalizer: null);
 
             var actionContext = new ActionContext();
-            var context = new ClientModelValidationContext(actionContext, metadata, provider);
+            var context = new ClientModelValidationContext(actionContext, metadata, provider, new AttributeDictionary());
 
             // Act
-            var rules = adapter.GetClientValidationRules(context);
+            adapter.AddValidation(context);
 
             // Assert
-            var rule = Assert.Single(rules);
+            Assert.Collection(
-            Assert.Equal("range", rule.ValidationType);
+                context.Attributes,
-            Assert.Equal(2, rule.ValidationParameters.Count);
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
-            Assert.Equal(0m, rule.ValidationParameters["min"]);
+                kvp => { Assert.Equal("data-val-range", kvp.Key); Assert.Equal(expectedMessage, kvp.Value); },
-            Assert.Equal(100m, rule.ValidationParameters["max"]);
+                kvp => { Assert.Equal("data-val-range-max", kvp.Key); Assert.Equal("100", kvp.Value); },
-            Assert.Equal(expectedMessage, rule.ErrorMessage);
+                kvp => { Assert.Equal("data-val-range-min", kvp.Key); Assert.Equal("0", kvp.Value); });
         }
 
         [Fact]
         [ReplaceCulture]
-        public void GetClientValidationRules_ReturnsValidationParameters()
+        public void AddValidation_WithLocalization()
         {
             // Arrange
             var provider = TestModelMetadataProvider.CreateDefaultProvider();
@@ -57,24 +58,58 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Validation
             var expectedMessage = "The field Length must be between 0 and 100.";
 
             var stringLocalizer = new Mock<IStringLocalizer>();
-            stringLocalizer.Setup(s => s[attribute.ErrorMessage, expectedProperties])
+            stringLocalizer
+                .Setup(s => s[attribute.ErrorMessage, expectedProperties])
                 .Returns(new LocalizedString(attribute.ErrorMessage, expectedMessage));
 
             var adapter = new RangeAttributeAdapter(attribute, stringLocalizer: stringLocalizer.Object);
 
             var actionContext = new ActionContext();
-            var context = new ClientModelValidationContext(actionContext, metadata, provider);
+            var context = new ClientModelValidationContext(actionContext, metadata, provider, new AttributeDictionary());
 
             // Act
-            var rules = adapter.GetClientValidationRules(context);
+            adapter.AddValidation(context);
 
             // Assert
-            var rule = Assert.Single(rules);
+            Assert.Collection(
-            Assert.Equal("range", rule.ValidationType);
+                context.Attributes,
-            Assert.Equal(2, rule.ValidationParameters.Count);
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
-            Assert.Equal(0m, rule.ValidationParameters["min"]);
+                kvp => { Assert.Equal("data-val-range", kvp.Key); Assert.Equal(expectedMessage, kvp.Value); },
-            Assert.Equal(100m, rule.ValidationParameters["max"]);
+                kvp => { Assert.Equal("data-val-range-max", kvp.Key); Assert.Equal("100", kvp.Value); },
-            Assert.Equal(expectedMessage, rule.ErrorMessage);
+                kvp => { Assert.Equal("data-val-range-min", kvp.Key); Assert.Equal("0", kvp.Value); });
+        }
+
+        [Fact]
+        [ReplaceCulture]
+        public void AddValidation_DoesNotTrounceExistingAttributes()
+        {
+            // Arrange
+            var provider = TestModelMetadataProvider.CreateDefaultProvider();
+            var metadata = provider.GetMetadataForProperty(typeof(string), "Length");
+
+            var attribute = new RangeAttribute(typeof(decimal), "0", "100");
+            attribute.ErrorMessage = "The field Length must be between {1} and {2}.";
+
+            var adapter = new RangeAttributeAdapter(attribute, stringLocalizer: null);
+
+            var actionContext = new ActionContext();
+            var context = new ClientModelValidationContext(actionContext, metadata, provider, new AttributeDictionary());
+
+            context.Attributes.Add("data-val", "original");
+            context.Attributes.Add("data-val-range", "original");
+            context.Attributes.Add("data-val-range-max", "original");
+            context.Attributes.Add("data-val-range-min", "original");
+
+            // Act
+            adapter.AddValidation(context);
+
+            // Assert
+            Assert.Collection(
+                context.Attributes,
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("original", kvp.Value); },
+                kvp => { Assert.Equal("data-val-range", kvp.Key); Assert.Equal("original", kvp.Value); },
+                kvp => { Assert.Equal("data-val-range-max", kvp.Key); Assert.Equal("original", kvp.Value); },
+                kvp => { Assert.Equal("data-val-range-min", kvp.Key); Assert.Equal("original", kvp.Value); });
         }
     }
 }

test/Microsoft.AspNetCore.Mvc.DataAnnotations.Test/Internal/RequiredAttributeAdapterTest.cs

@@ -4,6 +4,7 @@
 using System.ComponentModel.DataAnnotations;
 using Microsoft.AspNetCore.Mvc.ModelBinding;
 using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
+using Microsoft.AspNetCore.Mvc.ViewFeatures;
 using Microsoft.AspNetCore.Testing;
 using Microsoft.Extensions.Localization;
 using Moq;
@@ -15,7 +16,7 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
     {
         [Fact]
         [ReplaceCulture]
-        public void GetClientValidationRules_ReturnsValidationParameters_Localize()
+        public void AddValidation_AddsValidation_Localize()
         {
             // Arrange
             var provider = TestModelMetadataProvider.CreateDefaultProvider();
@@ -35,24 +36,24 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
             var adapter = new RequiredAttributeAdapter(attribute, stringLocalizer: stringLocalizer.Object);
 
             var actionContext = new ActionContext();
-            var context = new ClientModelValidationContext(actionContext, metadata, provider);
+            var context = new ClientModelValidationContext(actionContext, metadata, provider, new AttributeDictionary());
 
             // Act
-            var rules = adapter.GetClientValidationRules(context);
+            adapter.AddValidation(context);
 
             // Assert
-            var rule = Assert.Single(rules);
+            Assert.Collection(
-            Assert.Equal("required", rule.ValidationType);
+                context.Attributes,
-            Assert.Empty(rule.ValidationParameters);
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
-            Assert.Equal(expectedMessage, rule.ErrorMessage);
+                kvp => { Assert.Equal("data-val-required", kvp.Key); Assert.Equal(expectedMessage, kvp.Value); });
         }
 
         [Fact]
         [ReplaceCulture]
-        public void GetClientValidationRules_ReturnsValidationParameters()
+        public void AddValidation_AddsValidation()
         {
             // Arrange
-            var expected = ValidationAttributeUtil.GetRequiredErrorMessage("Length");
+            var expectedMessage = ValidationAttributeUtil.GetRequiredErrorMessage("Length");
             var provider = TestModelMetadataProvider.CreateDefaultProvider();
             var metadata = provider.GetMetadataForProperty(typeof(string), "Length");
 
@@ -60,16 +61,44 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
             var adapter = new RequiredAttributeAdapter(attribute, stringLocalizer: null);
 
             var actionContext = new ActionContext();
-            var context = new ClientModelValidationContext(actionContext, metadata, provider);
+            var context = new ClientModelValidationContext(actionContext, metadata, provider, new AttributeDictionary());
 
             // Act
-            var rules = adapter.GetClientValidationRules(context);
+            adapter.AddValidation(context);
 
             // Assert
-            var rule = Assert.Single(rules);
+            Assert.Collection(
-            Assert.Equal("required", rule.ValidationType);
+                context.Attributes,
-            Assert.Empty(rule.ValidationParameters);
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
-            Assert.Equal(expected, rule.ErrorMessage);
+                kvp => { Assert.Equal("data-val-required", kvp.Key); Assert.Equal(expectedMessage, kvp.Value); });
+        }
+
+        [Fact]
+        [ReplaceCulture]
+        public void AddValidation_DoesNotTrounceExistingAttributes()
+        {
+            // Arrange
+            var expectedMessage = ValidationAttributeUtil.GetRequiredErrorMessage("Length");
+            var provider = TestModelMetadataProvider.CreateDefaultProvider();
+            var metadata = provider.GetMetadataForProperty(typeof(string), "Length");
+
+            var attribute = new RequiredAttribute();
+            var adapter = new RequiredAttributeAdapter(attribute, stringLocalizer: null);
+
+            var actionContext = new ActionContext();
+            var context = new ClientModelValidationContext(actionContext, metadata, provider, new AttributeDictionary());
+
+            context.Attributes.Add("data-val", "original");
+            context.Attributes.Add("data-val-required", "original");
+
+            // Act
+            adapter.AddValidation(context);
+
+            // Assert
+            Assert.Collection(
+                context.Attributes,
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("original", kvp.Value); },
+                kvp => { Assert.Equal("data-val-required", kvp.Key); Assert.Equal("original", kvp.Value); });
         }
     }
 }

test/Microsoft.AspNetCore.Mvc.DataAnnotations.Test/Internal/StringLengthAttributeAdapterTest.cs

@@ -4,6 +4,7 @@
 using System.ComponentModel.DataAnnotations;
 using Microsoft.AspNetCore.Mvc.ModelBinding;
 using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
+using Microsoft.AspNetCore.Mvc.ViewFeatures;
 using Microsoft.AspNetCore.Testing;
 using Microsoft.Extensions.Localization;
 using Moq;
@@ -15,7 +16,7 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
     {
         [Fact]
         [ReplaceCulture]
-        public void GetClientValidationRules_WithMaxLength_ReturnsValidationParameters_Localize()
+        public void AddValidation_WithMaxLength_AddsAttributes_Localize()
         {
             // Arrange
             var provider = TestModelMetadataProvider.CreateDefaultProvider();
@@ -35,22 +36,23 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
             var adapter = new StringLengthAttributeAdapter(attribute, stringLocalizer: stringLocalizer.Object);
 
             var actionContext = new ActionContext();
-            var context = new ClientModelValidationContext(actionContext, metadata, provider);
+            var context = new ClientModelValidationContext(actionContext, metadata, provider, new AttributeDictionary());
 
             // Act
-            var rules = adapter.GetClientValidationRules(context);
+            adapter.AddValidation(context);
 
             // Assert
-            var rule = Assert.Single(rules);
+            Assert.Collection(
-            Assert.Equal("length", rule.ValidationType);
+                context.Attributes,
-            Assert.Equal(1, rule.ValidationParameters.Count);
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
-            Assert.Equal(8, rule.ValidationParameters["max"]);
+                kvp => { Assert.Equal("data-val-length", kvp.Key); Assert.Equal(expectedMessage, kvp.Value); },
-            Assert.Equal(expectedMessage, rule.ErrorMessage);
+                kvp => { Assert.Equal("data-val-length-max", kvp.Key); Assert.Equal("8", kvp.Value); });
+
         }
 
         [Fact]
         [ReplaceCulture]
-        public void GetClientValidationRules_WithMaxLength_ReturnsValidationParameters()
+        public void AddValidation_WithMaxLength_AddsAttributes()
         {
             // Arrange
             var provider = TestModelMetadataProvider.CreateDefaultProvider();
@@ -59,23 +61,25 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
             var attribute = new StringLengthAttribute(8);
             var adapter = new StringLengthAttributeAdapter(attribute, stringLocalizer: null);
 
+            var expectedMessage = attribute.FormatErrorMessage("Length");
+
             var actionContext = new ActionContext();
-            var context = new ClientModelValidationContext(actionContext, metadata, provider);
+            var context = new ClientModelValidationContext(actionContext, metadata, provider, new AttributeDictionary());
 
             // Act
-            var rules = adapter.GetClientValidationRules(context);
+            adapter.AddValidation(context);
 
             // Assert
-            var rule = Assert.Single(rules);
+            Assert.Collection(
-            Assert.Equal("length", rule.ValidationType);
+                context.Attributes,
-            Assert.Equal(1, rule.ValidationParameters.Count);
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
-            Assert.Equal(8, rule.ValidationParameters["max"]);
+                kvp => { Assert.Equal("data-val-length", kvp.Key); Assert.Equal(expectedMessage, kvp.Value); },
-            Assert.Equal(attribute.FormatErrorMessage("Length"), rule.ErrorMessage);
+                kvp => { Assert.Equal("data-val-length-max", kvp.Key); Assert.Equal("8", kvp.Value); });
         }
 
         [Fact]
         [ReplaceCulture]
-        public void GetClientValidationRules_WithMinAndMaxLength_ReturnsValidationParameters()
+        public void AddValidation_WithMinAndMaxLength_AddsAttributes()
         {
             // Arrange
             var provider = TestModelMetadataProvider.CreateDefaultProvider();
@@ -84,19 +88,80 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
             var attribute = new StringLengthAttribute(10) { MinimumLength = 3 };
             var adapter = new StringLengthAttributeAdapter(attribute, stringLocalizer: null);
 
+            var expectedMessage = attribute.FormatErrorMessage("Length");
+
             var actionContext = new ActionContext();
-            var context = new ClientModelValidationContext(actionContext, metadata, provider);
+            var context = new ClientModelValidationContext(actionContext, metadata, provider, new AttributeDictionary());
 
             // Act
-            var rules = adapter.GetClientValidationRules(context);
+            adapter.AddValidation(context);
 
             // Assert
-            var rule = Assert.Single(rules);
+            Assert.Collection(
-            Assert.Equal("length", rule.ValidationType);
+                context.Attributes,
-            Assert.Equal(2, rule.ValidationParameters.Count);
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
-            Assert.Equal(3, rule.ValidationParameters["min"]);
+                kvp => { Assert.Equal("data-val-length", kvp.Key); Assert.Equal(expectedMessage, kvp.Value); },
-            Assert.Equal(10, rule.ValidationParameters["max"]);
+                kvp => { Assert.Equal("data-val-length-max", kvp.Key); Assert.Equal("10", kvp.Value); },
-            Assert.Equal(attribute.FormatErrorMessage("Length"), rule.ErrorMessage);
+                kvp => { Assert.Equal("data-val-length-min", kvp.Key); Assert.Equal("3", kvp.Value); });
+        }
+
+        [Fact]
+        [ReplaceCulture]
+        public void AddValidation_WithMaxLength_AtIntMaxValue_AddsAttributes()
+        {
+            // Arrange
+            var provider = TestModelMetadataProvider.CreateDefaultProvider();
+            var metadata = provider.GetMetadataForProperty(typeof(string), "Length");
+
+            var attribute = new StringLengthAttribute(int.MaxValue);
+            var adapter = new StringLengthAttributeAdapter(attribute, stringLocalizer: null);
+
+            var expectedMessage = attribute.FormatErrorMessage("Length");
+
+            var actionContext = new ActionContext();
+            var context = new ClientModelValidationContext(actionContext, metadata, provider, new AttributeDictionary());
+
+            // Act
+            adapter.AddValidation(context);
+
+            // Assert
+            Assert.Collection(
+                context.Attributes,
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
+                kvp => { Assert.Equal("data-val-length", kvp.Key); Assert.Equal(expectedMessage, kvp.Value); });
+        }
+
+        [Fact]
+        [ReplaceCulture]
+        public void AddValidation_DoesNotTrounceExistingAttributes()
+        {
+            // Arrange
+            var provider = TestModelMetadataProvider.CreateDefaultProvider();
+            var metadata = provider.GetMetadataForProperty(typeof(string), "Length");
+
+            var attribute = new StringLengthAttribute(10) { MinimumLength = 3 };
+            var adapter = new StringLengthAttributeAdapter(attribute, stringLocalizer: null);
+
+            var expectedMessage = attribute.FormatErrorMessage("Length");
+
+            var actionContext = new ActionContext();
+            var context = new ClientModelValidationContext(actionContext, metadata, provider, new AttributeDictionary());
+
+            context.Attributes.Add("data-val", "original");
+            context.Attributes.Add("data-val-length", "original");
+            context.Attributes.Add("data-val-length-max", "original");
+            context.Attributes.Add("data-val-length-min", "original");
+
+            // Act
+            adapter.AddValidation(context);
+
+            // Assert
+            Assert.Collection(
+                context.Attributes,
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("original", kvp.Value); },
+                kvp => { Assert.Equal("data-val-length", kvp.Key); Assert.Equal("original", kvp.Value); },
+                kvp => { Assert.Equal("data-val-length-max", kvp.Key); Assert.Equal("original", kvp.Value); },
+                kvp => { Assert.Equal("data-val-length-min", kvp.Key); Assert.Equal("original", kvp.Value); });
         }
     }
 }

test/Microsoft.AspNetCore.Mvc.DataAnnotations.Test/Internal/ValidationAttributeAdapterOfTAttributeTest.cs

@@ -59,7 +59,7 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
                 : base(attribute, stringLocalizer)
             { }
 
-            public override IEnumerable<ModelClientValidationRule> GetClientValidationRules(ClientModelValidationContext context)
+            public override void AddValidation(ClientModelValidationContext context)
             {
                 throw new NotImplementedException();
             }

test/Microsoft.AspNetCore.Mvc.DataAnnotations.Test/Internal/ValidationAttributeAdapterProviderTest.cs

@@ -64,10 +64,10 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
             get
             {
                 return new TheoryData<ValidationAttribute, string> {
-                    { new UrlAttribute(), "url" },
+                    { new UrlAttribute(), "data-val-url" },
-                    { new CreditCardAttribute(), "creditcard" },
+                    { new CreditCardAttribute(), "data-val-creditcard" },
-                    { new EmailAddressAttribute(), "email" },
+                    { new EmailAddressAttribute(), "data-val-email" },
-                    { new PhoneAttribute(), "phone" }
+                    { new PhoneAttribute(), "data-val-phone" }
                 };
             }
         }

test/Microsoft.AspNetCore.Mvc.TagHelpers.Test/TestableHtmlGenerator.cs

@@ -95,12 +95,13 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers
             return tagBuilder;
         }
 
-        protected override IDictionary<string, object> GetValidationAttributes(
+        protected override void AddValidationAttributes(
             ViewContext viewContext,
+            TagBuilder tagBuilder,
             ModelExplorer modelExplorer,
-            string name)
+            string expression)
         {
-            return ValidationAttributes;
+            tagBuilder.MergeAttributes(ValidationAttributes);
         }
 
         private static IOptions<MvcViewOptions> GetOptions()

test/Microsoft.AspNetCore.Mvc.ViewFeatures.Test/Internal/DefaultEditorTemplatesTest.cs

@@ -1085,13 +1085,6 @@ Environment.NewLine;
                 throw new NotImplementedException();
             }
 
-            public IEnumerable<ModelClientValidationRule> GetClientValidationRules(
-                ModelExplorer modelExplorer,
-                string name)
-            {
-                return Enumerable.Empty<ModelClientValidationRule>();
-            }
-
             public IEnumerable<SelectListItem> GetEnumSelectList<TEnum>() where TEnum : struct
             {
                 throw new NotImplementedException();

test/Microsoft.AspNetCore.Mvc.ViewFeatures.Test/RemoteAttributeTest.cs

@@ -9,6 +9,7 @@ using Microsoft.AspNetCore.Mvc.Abstractions;
 using Microsoft.AspNetCore.Mvc.ModelBinding;
 using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
 using Microsoft.AspNetCore.Mvc.Routing;
+using Microsoft.AspNetCore.Mvc.ViewFeatures;
 using Microsoft.AspNetCore.Routing;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Logging;
@@ -184,19 +185,19 @@ namespace Microsoft.AspNetCore.Mvc
         }
 
         [Fact]
-        public void GetClientValidationRules_WithBadRouteName_Throws()
+        public void AddValidation_WithBadRouteName_Throws()
         {
             // Arrange
             var attribute = new RemoteAttribute("nonexistentRoute");
             var context = GetValidationContextWithArea(currentArea: null);
 
             // Act & Assert
-            var exception = Assert.Throws<InvalidOperationException>(() => attribute.GetClientValidationRules(context));
+            var exception = Assert.Throws<InvalidOperationException>(() => attribute.AddValidation(context));
             Assert.Equal("No URL for remote validation could be found.", exception.Message);
         }
 
         [Fact]
-        public void GetClientValidationRules_WithRoute_CallsUrlHelperWithExpectedValues()
+        public void AddValidation_WithRoute_CallsUrlHelperWithExpectedValues()
         {
             // Arrange
             var routeName = "RouteName";
@@ -205,21 +206,23 @@ namespace Microsoft.AspNetCore.Mvc
             var urlHelper = new MockUrlHelper(url, routeName);
             var context = GetValidationContext(urlHelper);
 
-            // Act & Assert
+            // Act
-            var rule = Assert.Single(attribute.GetClientValidationRules(context));
+            attribute.AddValidation(context);
-            Assert.Equal("remote", rule.ValidationType);
-            Assert.Equal("'Length' is invalid.", rule.ErrorMessage);
 
-            Assert.Equal(2, rule.ValidationParameters.Count);
+            // Assert
-            Assert.Equal("*.Length", rule.ValidationParameters["additionalfields"]);
+            Assert.Collection(
-            Assert.Equal(url, rule.ValidationParameters["url"]);
+                context.Attributes,
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
+                kvp => { Assert.Equal("data-val-remote", kvp.Key); Assert.Equal("'Length' is invalid.", kvp.Value); },
+                kvp => { Assert.Equal("data-val-remote-additionalfields", kvp.Key); Assert.Equal("*.Length", kvp.Value); },
+                kvp => { Assert.Equal("data-val-remote-url", kvp.Key); Assert.Equal(url, kvp.Value); });
 
             var routeDictionary = Assert.IsType<RouteValueDictionary>(urlHelper.RouteValues);
             Assert.Empty(routeDictionary);
         }
 
         [Fact]
-        public void GetClientValidationRules_WithActionController_CallsUrlHelperWithExpectedValues()
+        public void AddValidation_WithActionController_CallsUrlHelperWithExpectedValues()
         {
             // Arrange
             var attribute = new RemoteAttribute("Action", "Controller");
@@ -227,14 +230,16 @@ namespace Microsoft.AspNetCore.Mvc
             var urlHelper = new MockUrlHelper(url, routeName: null);
             var context = GetValidationContext(urlHelper);
 
-            // Act & Assert
+            // Act
-            var rule = Assert.Single(attribute.GetClientValidationRules(context));
+            attribute.AddValidation(context);
-            Assert.Equal("remote", rule.ValidationType);
-            Assert.Equal("'Length' is invalid.", rule.ErrorMessage);
 
-            Assert.Equal(2, rule.ValidationParameters.Count);
+            // Assert
-            Assert.Equal("*.Length", rule.ValidationParameters["additionalfields"]);
+            Assert.Collection(
-            Assert.Equal(url, rule.ValidationParameters["url"]);
+                context.Attributes,
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
+                kvp => { Assert.Equal("data-val-remote", kvp.Key); Assert.Equal("'Length' is invalid.", kvp.Value); },
+                kvp => { Assert.Equal("data-val-remote-additionalfields", kvp.Key); Assert.Equal("*.Length", kvp.Value); },
+                kvp => { Assert.Equal("data-val-remote-url", kvp.Key); Assert.Equal(url, kvp.Value); });
 
             var routeDictionary = Assert.IsType<RouteValueDictionary>(urlHelper.RouteValues);
             Assert.Equal(2, routeDictionary.Count);
@@ -243,7 +248,7 @@ namespace Microsoft.AspNetCore.Mvc
         }
 
         [Fact]
-        public void GetClientValidationRules_WithActionController_PropertiesSet_CallsUrlHelperWithExpectedValues()
+        public void AddValidation_WithActionController_PropertiesSet_CallsUrlHelperWithExpectedValues()
         {
             // Arrange
             var attribute = new RemoteAttribute("Action", "Controller")
@@ -255,15 +260,21 @@ namespace Microsoft.AspNetCore.Mvc
             var urlHelper = new MockUrlHelper(url, routeName: null);
             var context = GetValidationContext(urlHelper);
 
-            // Act & Assert
+            // Act
-            var rule = Assert.Single(attribute.GetClientValidationRules(context));
+            attribute.AddValidation(context);
-            Assert.Equal("remote", rule.ValidationType);
-            Assert.Equal("'Length' is invalid.", rule.ErrorMessage);
 
-            Assert.Equal(3, rule.ValidationParameters.Count);
+            // Assert
-            Assert.Equal("*.Length,*.Password,*.ConfirmPassword", rule.ValidationParameters["additionalfields"]);
+            Assert.Collection(
-            Assert.Equal("POST", rule.ValidationParameters["type"]);
+                context.Attributes,
-            Assert.Equal(url, rule.ValidationParameters["url"]);
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
+                kvp => { Assert.Equal("data-val-remote", kvp.Key); Assert.Equal("'Length' is invalid.", kvp.Value); },
+                kvp =>
+                {
+                    Assert.Equal("data-val-remote-additionalfields", kvp.Key);
+                    Assert.Equal("*.Length,*.Password,*.ConfirmPassword", kvp.Value);
+                },
+                kvp => { Assert.Equal("data-val-remote-type", kvp.Key); Assert.Equal("POST", kvp.Value); },
+                kvp => { Assert.Equal("data-val-remote-url", kvp.Key); Assert.Equal(url, kvp.Value); });
 
             var routeDictionary = Assert.IsType<RouteValueDictionary>(urlHelper.RouteValues);
             Assert.Equal(2, routeDictionary.Count);
@@ -272,7 +283,7 @@ namespace Microsoft.AspNetCore.Mvc
         }
 
         [Fact]
-        public void GetClientValidationRules_WithActionControllerArea_CallsUrlHelperWithExpectedValues()
+        public void AddValidation_WithActionControllerArea_CallsUrlHelperWithExpectedValues()
         {
             // Arrange
             var attribute = new RemoteAttribute("Action", "Controller", "Test")
@@ -283,15 +294,21 @@ namespace Microsoft.AspNetCore.Mvc
             var urlHelper = new MockUrlHelper(url, routeName: null);
             var context = GetValidationContext(urlHelper);
 
-            // Act & Assert
+            // Act
-            var rule = Assert.Single(attribute.GetClientValidationRules(context));
+            attribute.AddValidation(context);
-            Assert.Equal("remote", rule.ValidationType);
-            Assert.Equal("'Length' is invalid.", rule.ErrorMessage);
 
-            Assert.Equal(3, rule.ValidationParameters.Count);
+            // Assert
-            Assert.Equal("*.Length", rule.ValidationParameters["additionalfields"]);
+            Assert.Collection(
-            Assert.Equal("POST", rule.ValidationParameters["type"]);
+                context.Attributes,
-            Assert.Equal(url, rule.ValidationParameters["url"]);
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
+                kvp => { Assert.Equal("data-val-remote", kvp.Key); Assert.Equal("'Length' is invalid.", kvp.Value); },
+                kvp =>
+                {
+                    Assert.Equal("data-val-remote-additionalfields", kvp.Key);
+                    Assert.Equal("*.Length", kvp.Value);
+                },
+                kvp => { Assert.Equal("data-val-remote-type", kvp.Key); Assert.Equal("POST", kvp.Value); },
+                kvp => { Assert.Equal("data-val-remote-url", kvp.Key); Assert.Equal(url, kvp.Value); });
 
             var routeDictionary = Assert.IsType<RouteValueDictionary>(urlHelper.RouteValues);
             Assert.Equal(3, routeDictionary.Count);
@@ -302,138 +319,203 @@ namespace Microsoft.AspNetCore.Mvc
 
         // Root area is current in this case.
         [Fact]
-        public void GetClientValidationRules_WithActionController_FindsControllerInCurrentArea()
+        public void AddValidation_WithActionController_FindsControllerInCurrentArea()
         {
             // Arrange
             var attribute = new RemoteAttribute("Action", "Controller");
             var context = GetValidationContextWithArea(currentArea: null);
 
-            // Act & Assert
+            // Act
-            var rule = Assert.Single(attribute.GetClientValidationRules(context));
+            attribute.AddValidation(context);
-            Assert.Equal("remote", rule.ValidationType);
-            Assert.Equal("'Length' is invalid.", rule.ErrorMessage);
 
-            Assert.Equal(2, rule.ValidationParameters.Count);
+            // Assert
-            Assert.Equal("*.Length", rule.ValidationParameters["additionalfields"]);
+            Assert.Collection(
-            Assert.Equal("/UrlEncode[[Controller]]/UrlEncode[[Action]]", rule.ValidationParameters["url"]);
+                context.Attributes,
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
+                kvp => { Assert.Equal("data-val-remote", kvp.Key); Assert.Equal("'Length' is invalid.", kvp.Value); },
+                kvp => { Assert.Equal("data-val-remote-additionalfields", kvp.Key); Assert.Equal("*.Length", kvp.Value); },
+                kvp =>
+                {
+                    Assert.Equal("data-val-remote-url", kvp.Key);
+                    Assert.Equal("/UrlEncode[[Controller]]/UrlEncode[[Action]]", kvp.Value);
+                });
         }
 
         // Test area is current in this case.
         [Fact]
-        public void GetClientValidationRules_WithActionControllerInArea_FindsControllerInCurrentArea()
+        public void AddValidation_WithActionControllerInArea_FindsControllerInCurrentArea()
         {
             // Arrange
             var attribute = new RemoteAttribute("Action", "Controller");
             var context = GetValidationContextWithArea(currentArea: "Test");
 
-            // Act & Assert
+            // Act
-            var rule = Assert.Single(attribute.GetClientValidationRules(context));
+            attribute.AddValidation(context);
-            Assert.Equal("remote", rule.ValidationType);
-            Assert.Equal("'Length' is invalid.", rule.ErrorMessage);
 
-            Assert.Equal(2, rule.ValidationParameters.Count);
+            // Assert
-            Assert.Equal("*.Length", rule.ValidationParameters["additionalfields"]);
+            Assert.Collection(
-            Assert.Equal(
+                context.Attributes,
-                "/UrlEncode[[Test]]/UrlEncode[[Controller]]/UrlEncode[[Action]]",
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
-                rule.ValidationParameters["url"]);
+                kvp => { Assert.Equal("data-val-remote", kvp.Key); Assert.Equal("'Length' is invalid.", kvp.Value); },
+                kvp => { Assert.Equal("data-val-remote-additionalfields", kvp.Key); Assert.Equal("*.Length", kvp.Value); },
+                kvp =>
+                {
+                    Assert.Equal("data-val-remote-url", kvp.Key);
+                    Assert.Equal("/UrlEncode[[Test]]/UrlEncode[[Controller]]/UrlEncode[[Action]]", kvp.Value);
+                });
         }
 
         // Explicit reference to the (current) root area.
         [Theory]
         [MemberData(nameof(NullOrEmptyNames))]
-        public void GetClientValidationRules_WithActionControllerArea_FindsControllerInRootArea(string areaName)
+        public void AddValidation_WithActionControllerArea_FindsControllerInRootArea(string areaName)
         {
             // Arrange
             var attribute = new RemoteAttribute("Action", "Controller", areaName);
             var context = GetValidationContextWithArea(currentArea: null);
 
-            // Act & Assert
+            // Act
-            var rule = Assert.Single(attribute.GetClientValidationRules(context));
+            attribute.AddValidation(context);
-            Assert.Equal("remote", rule.ValidationType);
-            Assert.Equal("'Length' is invalid.", rule.ErrorMessage);
 
-            Assert.Equal(2, rule.ValidationParameters.Count);
+            // Assert
-            Assert.Equal("*.Length", rule.ValidationParameters["additionalfields"]);
+            Assert.Collection(
-            Assert.Equal("/UrlEncode[[Controller]]/UrlEncode[[Action]]", rule.ValidationParameters["url"]);
+                context.Attributes,
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
+                kvp => { Assert.Equal("data-val-remote", kvp.Key); Assert.Equal("'Length' is invalid.", kvp.Value); },
+                kvp => { Assert.Equal("data-val-remote-additionalfields", kvp.Key); Assert.Equal("*.Length", kvp.Value); },
+                kvp =>
+                {
+                    Assert.Equal("data-val-remote-url", kvp.Key);
+                    Assert.Equal("/UrlEncode[[Controller]]/UrlEncode[[Action]]", kvp.Value);
+                });
         }
 
         // Test area is current in this case.
         [Theory]
         [MemberData(nameof(NullOrEmptyNames))]
-        public void GetClientValidationRules_WithActionControllerAreaInArea_FindsControllerInRootArea(string areaName)
+        public void AddValidation_WithActionControllerAreaInArea_FindsControllerInRootArea(string areaName)
         {
             // Arrange
             var attribute = new RemoteAttribute("Action", "Controller", areaName);
             var context = GetValidationContextWithArea(currentArea: "Test");
 
-            // Act & Assert
+            // Act
-            var rule = Assert.Single(attribute.GetClientValidationRules(context));
+            attribute.AddValidation(context);
-            Assert.Equal("remote", rule.ValidationType);
-            Assert.Equal("'Length' is invalid.", rule.ErrorMessage);
 
-            Assert.Equal(2, rule.ValidationParameters.Count);
+            // Assert
-            Assert.Equal("*.Length", rule.ValidationParameters["additionalfields"]);
+            Assert.Collection(
-            Assert.Equal("/UrlEncode[[Controller]]/UrlEncode[[Action]]", rule.ValidationParameters["url"]);
+                context.Attributes,
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
+                kvp => { Assert.Equal("data-val-remote", kvp.Key); Assert.Equal("'Length' is invalid.", kvp.Value); },
+                kvp => { Assert.Equal("data-val-remote-additionalfields", kvp.Key); Assert.Equal("*.Length", kvp.Value); },
+                kvp =>
+                {
+                    Assert.Equal("data-val-remote-url", kvp.Key);
+                    Assert.Equal("/UrlEncode[[Controller]]/UrlEncode[[Action]]", kvp.Value);
+                });
         }
 
         // Root area is current in this case.
         [Fact]
-        public void GetClientValidationRules_WithActionControllerArea_FindsControllerInNamedArea()
+        public void AddValidation_WithActionControllerArea_FindsControllerInNamedArea()
         {
             // Arrange
             var attribute = new RemoteAttribute("Action", "Controller", "Test");
             var context = GetValidationContextWithArea(currentArea: null);
 
-            // Act & Assert
+            // Act
-            var rule = Assert.Single(attribute.GetClientValidationRules(context));
+            attribute.AddValidation(context);
-            Assert.Equal("remote", rule.ValidationType);
-            Assert.Equal("'Length' is invalid.", rule.ErrorMessage);
 
-            Assert.Equal(2, rule.ValidationParameters.Count);
+            // Assert
-            Assert.Equal("*.Length", rule.ValidationParameters["additionalfields"]);
+            Assert.Collection(
-            Assert.Equal(
+                context.Attributes,
-                "/UrlEncode[[Test]]/UrlEncode[[Controller]]/UrlEncode[[Action]]",
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
-                rule.ValidationParameters["url"]);
+                kvp => { Assert.Equal("data-val-remote", kvp.Key); Assert.Equal("'Length' is invalid.", kvp.Value); },
+                kvp => { Assert.Equal("data-val-remote-additionalfields", kvp.Key); Assert.Equal("*.Length", kvp.Value); },
+                kvp =>
+                {
+                    Assert.Equal("data-val-remote-url", kvp.Key);
+                    Assert.Equal("/UrlEncode[[Test]]/UrlEncode[[Controller]]/UrlEncode[[Action]]", kvp.Value);
+                });
         }
 
         // Explicit reference to the current (Test) area.
         [Fact]
-        public void GetClientValidationRules_WithActionControllerAreaInArea_FindsControllerInNamedArea()
+        public void AddValidation_WithActionControllerAreaInArea_FindsControllerInNamedArea()
         {
             // Arrange
             var attribute = new RemoteAttribute("Action", "Controller", "Test");
             var context = GetValidationContextWithArea(currentArea: "Test");
 
-            // Act & Assert
+            // Act
-            var rule = Assert.Single(attribute.GetClientValidationRules(context));
+            attribute.AddValidation(context);
-            Assert.Equal("remote", rule.ValidationType);
-            Assert.Equal("'Length' is invalid.", rule.ErrorMessage);
 
-            Assert.Equal(2, rule.ValidationParameters.Count);
+            // Assert
-            Assert.Equal("*.Length", rule.ValidationParameters["additionalfields"]);
+            Assert.Collection(
-            Assert.Equal(
+                context.Attributes,
-                "/UrlEncode[[Test]]/UrlEncode[[Controller]]/UrlEncode[[Action]]",
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
-                rule.ValidationParameters["url"]);
+                kvp => { Assert.Equal("data-val-remote", kvp.Key); Assert.Equal("'Length' is invalid.", kvp.Value); },
+                kvp => { Assert.Equal("data-val-remote-additionalfields", kvp.Key); Assert.Equal("*.Length", kvp.Value); },
+                kvp =>
+                {
+                    Assert.Equal("data-val-remote-url", kvp.Key);
+                    Assert.Equal("/UrlEncode[[Test]]/UrlEncode[[Controller]]/UrlEncode[[Action]]", kvp.Value);
+                });
         }
 
         // Test area is current in this case.
         [Fact]
-        public void GetClientValidationRules_WithActionControllerAreaInArea_FindsControllerInDifferentArea()
+        public void AddValidation_WithActionControllerAreaInArea_FindsControllerInDifferentArea()
         {
             // Arrange
             var attribute = new RemoteAttribute("Action", "Controller", "AnotherArea");
             var context = GetValidationContextWithArea(currentArea: "Test");
 
-            // Act & Assert
+            // Act
-            var rule = Assert.Single(attribute.GetClientValidationRules(context));
+            attribute.AddValidation(context);
-            Assert.Equal("remote", rule.ValidationType);
-            Assert.Equal("'Length' is invalid.", rule.ErrorMessage);
 
-            Assert.Equal(2, rule.ValidationParameters.Count);
+            // Assert
-            Assert.Equal("*.Length", rule.ValidationParameters["additionalfields"]);
+            Assert.Collection(
-            Assert.Equal(
+                context.Attributes,
-                "/UrlEncode[[AnotherArea]]/UrlEncode[[Controller]]/UrlEncode[[Action]]",
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("true", kvp.Value); },
-                rule.ValidationParameters["url"]);
+                kvp => { Assert.Equal("data-val-remote", kvp.Key); Assert.Equal("'Length' is invalid.", kvp.Value); },
+                kvp => { Assert.Equal("data-val-remote-additionalfields", kvp.Key); Assert.Equal("*.Length", kvp.Value); },
+                kvp =>
+                {
+                    Assert.Equal("data-val-remote-url", kvp.Key);
+                    Assert.Equal("/UrlEncode[[AnotherArea]]/UrlEncode[[Controller]]/UrlEncode[[Action]]", kvp.Value);
+                });
+        }
+
+        // Test area is current in this case.
+        [Fact]
+        public void AddValidation_DoesNotTrounceExistingAttributes()
+        {
+            // Arrange
+            var attribute = new RemoteAttribute("Action", "Controller", "AnotherArea")
+            {
+                HttpMethod = "PUT",
+            };
+
+            var context = GetValidationContextWithArea(currentArea: "Test");
+
+            context.Attributes.Add("data-val", "original");
+            context.Attributes.Add("data-val-remote", "original");
+            context.Attributes.Add("data-val-remote-additionalfields", "original");
+            context.Attributes.Add("data-val-remote-type", "original");
+            context.Attributes.Add("data-val-remote-url", "original");
+
+            // Act
+            attribute.AddValidation(context);
+
+            // Assert
+            Assert.Collection(
+                context.Attributes,
+                kvp => { Assert.Equal("data-val", kvp.Key); Assert.Equal("original", kvp.Value); },
+                kvp => { Assert.Equal("data-val-remote", kvp.Key); Assert.Equal("original", kvp.Value); },
+                kvp => { Assert.Equal("data-val-remote-additionalfields", kvp.Key); Assert.Equal("original", kvp.Value); },
+                kvp => { Assert.Equal("data-val-remote-type", kvp.Key); Assert.Equal("original", kvp.Value); },
+                kvp => { Assert.Equal("data-val-remote-url", kvp.Key); Assert.Equal("original", kvp.Value); });
         }
 
         private static ClientModelValidationContext GetValidationContext(IUrlHelper urlHelper)
@@ -455,7 +537,11 @@ namespace Microsoft.AspNetCore.Mvc
                 },
             };
 
-            return new ClientModelValidationContext(actionContext, _metadata, _metadataProvider);
+            return new ClientModelValidationContext(
+                actionContext,
+                _metadata,
+                _metadataProvider,
+                new AttributeDictionary());
         }
 
         private static ClientModelValidationContext GetValidationContextWithArea(string currentArea)
@@ -499,7 +585,11 @@ namespace Microsoft.AspNetCore.Mvc
                 },
             };
 
-            return new ClientModelValidationContext(actionContext, _metadata, _metadataProvider);
+            return new ClientModelValidationContext(
+                 actionContext,
+                 _metadata,
+                 _metadataProvider,
+                 new AttributeDictionary());
         }
 
         private static IRouter GetRouteCollectionWithArea(IServiceProvider serviceProvider)