aspnetcore/src/Microsoft.AspNetCore.Mvc.ViewFeatures/ViewFeatures/ViewDataDictionary.cs

// 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;
using System.Collections.Generic;
using System.Globalization;
#if NETSTANDARD1_6
using System.Reflection;
#endif
using Microsoft.AspNetCore.Mvc.ModelBinding;
using Microsoft.AspNetCore.Mvc.ModelBinding.Metadata;
using Microsoft.Extensions.Internal;

namespace Microsoft.AspNetCore.Mvc.ViewFeatures
{
    public class ViewDataDictionary : IDictionary<string, object>
    {
        private readonly IDictionary<string, object> _data;
        private readonly Type _declaredModelType;
        private readonly IModelMetadataProvider _metadataProvider;

        /// <summary>
        /// Initializes a new instance of the <see cref="ViewDataDictionary"/> class.
        /// </summary>
        /// <param name="metadataProvider">
        /// <see cref="IModelMetadataProvider"/> instance used to create <see cref="ViewFeatures.ModelExplorer"/>
        /// instances.
        /// </param>
        /// <param name="modelState"><see cref="ModelStateDictionary"/> instance for this scope.</param>
        /// <remarks>For use when creating a <see cref="ViewDataDictionary"/> for a new top-level scope.</remarks>
        public ViewDataDictionary(
            IModelMetadataProvider metadataProvider,
            ModelStateDictionary modelState)
            : this(metadataProvider, modelState, declaredModelType: typeof(object))
        {
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="ViewDataDictionary"/> class based entirely on an existing
        /// instance.
        /// </summary>
        /// <param name="source"><see cref="ViewDataDictionary"/> instance to copy initial values from.</param>
        /// <remarks>
        /// <para>
        /// For use when copying a <see cref="ViewDataDictionary"/> instance and the declared <see cref="Model"/>
        /// <see cref="Type"/> will not change e.g. when copying from a <see cref="ViewDataDictionary{TModel}"/>
        /// instance to a base <see cref="ViewDataDictionary"/> instance.
        /// </para>
        /// <para>
        /// This constructor should not be used in any context where <see cref="Model"/> may be set to a value
        /// incompatible with the declared type of <paramref name="source"/>.
        /// </para>
        /// </remarks>
        public ViewDataDictionary(ViewDataDictionary source)
            : this(source, source.Model, source._declaredModelType)
        {
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="ViewDataDictionary"/> class.
        /// </summary>
        /// <param name="metadataProvider">
        /// <see cref="IModelMetadataProvider"/> instance used to create <see cref="ViewFeatures.ModelExplorer"/>
        /// instances.
        /// </param>
        /// <remarks>Internal for testing.</remarks>
        internal ViewDataDictionary(IModelMetadataProvider metadataProvider)
            : this(metadataProvider, new ModelStateDictionary())
        {
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="ViewDataDictionary"/> class.
        /// </summary>
        /// <param name="metadataProvider">
        /// <see cref="IModelMetadataProvider"/> instance used to create <see cref="ViewFeatures.ModelExplorer"/>
        /// instances.
        /// </param>
        /// <param name="declaredModelType">
        /// <see cref="Type"/> of <see cref="Model"/> values expected. Used to set <see cref="ModelMetadata"/>.
        /// </param>
        /// <remarks>
        /// For use when creating a derived <see cref="ViewDataDictionary"/> for a new top-level scope.
        /// </remarks>
        protected ViewDataDictionary(
            IModelMetadataProvider metadataProvider,
            Type declaredModelType)
            : this(metadataProvider, new ModelStateDictionary(), declaredModelType)
        {
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="ViewDataDictionary"/> class.
        /// </summary>
        /// <param name="metadataProvider">
        /// <see cref="IModelMetadataProvider"/> instance used to create <see cref="ViewFeatures.ModelExplorer"/>
        /// instances.
        /// </param>
        /// <param name="modelState"><see cref="ModelStateDictionary"/> instance for this scope.</param>
        /// <param name="declaredModelType">
        /// <see cref="Type"/> of <see cref="Model"/> values expected. Used to set <see cref="ModelMetadata"/>.
        /// </param>
        /// <remarks>
        /// For use when creating a derived <see cref="ViewDataDictionary"/> for a new top-level scope.
        /// </remarks>
        // This is the core constructor called when Model is unknown.
        protected ViewDataDictionary(
            IModelMetadataProvider metadataProvider,
            ModelStateDictionary modelState,
            Type declaredModelType)
            : this(metadataProvider,
                   modelState,
                   declaredModelType,
                   data: new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase),
                   templateInfo: new TemplateInfo())
        {
            if (metadataProvider == null)
            {
                throw new ArgumentNullException(nameof(metadataProvider));
            }

            if (modelState == null)
            {
                throw new ArgumentNullException(nameof(modelState));
            }

            if (declaredModelType == null)
            {
                throw new ArgumentNullException(nameof(declaredModelType));
            }

            // Base ModelMetadata on the declared type.
            ModelExplorer = _metadataProvider.GetModelExplorerForType(declaredModelType, model: null);
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="ViewDataDictionary"/> class based in part on an existing
        /// instance.
        /// </summary>
        /// <param name="source"><see cref="ViewDataDictionary"/> instance to copy initial values from.</param>
        /// <param name="declaredModelType">
        /// <see cref="Type"/> of <see cref="Model"/> values expected. Used to set <see cref="ModelMetadata"/>.
        /// </param>
        /// <remarks>
        /// <para>
        /// For use when copying a <see cref="ViewDataDictionary"/> instance and new instance's declared
        /// <see cref="Model"/> <see cref="Type"/> is known but <see cref="Model"/> should be copied from the existing
        /// instance e.g. when copying from a base <see cref="ViewDataDictionary"/> instance to a
        /// <see cref="ViewDataDictionary{TModel}"/> instance.
        /// </para>
        /// <para>
        /// This constructor may <c>throw</c> if <c>source.Model</c> is non-<c>null</c> and incompatible with
        /// <paramref name="declaredModelType"/>. Pass <c>model: null</c> to
        /// <see cref="ViewDataDictionary(ViewDataDictionary, object, Type)"/> to ignore <c>source.Model</c>.
        /// </para>
        /// </remarks>
        protected ViewDataDictionary(ViewDataDictionary source, Type declaredModelType)
            : this(source, model: source.Model, declaredModelType: declaredModelType)
        {
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="ViewDataDictionary"/> class based in part on an existing
        /// instance. This constructor is careful to avoid exceptions <see cref="SetModel"/> may throw when
        /// <paramref name="model"/> is <c>null</c>.
        /// </summary>
        /// <param name="source"><see cref="ViewDataDictionary"/> instance to copy initial values from.</param>
        /// <param name="model">Value for the <see cref="Model"/> property.</param>
        /// <param name="declaredModelType">
        /// <see cref="Type"/> of <see cref="Model"/> values expected. Used to set <see cref="ModelMetadata"/>.
        /// </param>
        /// <remarks>
        /// <para>
        /// For use when copying a <see cref="ViewDataDictionary"/> instance and new instance's declared
        /// <see cref="Model"/> <see cref="Type"/> and <see cref="Model"/> are known.
        /// </para>
        /// <para>
        /// This constructor may <c>throw</c> if <paramref name="model"/> is non-<c>null</c> and incompatible with
        /// <paramref name="declaredModelType"/>.
        /// </para>
        /// </remarks>
        // This is the core constructor called when Model is known.
        protected ViewDataDictionary(ViewDataDictionary source, object model, Type declaredModelType)
            : this(source._metadataProvider,
                   source.ModelState,
                   declaredModelType,
                   data: new CopyOnWriteDictionary<string, object>(source, StringComparer.OrdinalIgnoreCase),
                   templateInfo: new TemplateInfo(source.TemplateInfo))
        {
            if (source == null)
            {
                throw new ArgumentNullException(nameof(source));
            }

            // A non-null Model must always be assignable to both _declaredModelType and ModelMetadata.ModelType.
            //
            // ModelMetadata.ModelType should also be assignable to _declaredModelType. Though corner cases exist such
            // as a ViewDataDictionary<List<int>> holding information about an IEnumerable<int> property (because an
            // @model directive matched the runtime type though the view's name did not), we'll throw away the property
            // metadata in those cases -- preserving invariant that ModelType can be assigned to _declaredModelType.
            //
            // More generally, since defensive copies to base VDD and VDD<object> abound, it's important to preserve
            // metadata despite _declaredModelType changes.
            var modelType = model?.GetType();
            var modelOrDeclaredType = modelType ?? declaredModelType;
            if (source.ModelMetadata.MetadataKind == ModelMetadataKind.Type &&
                source.ModelMetadata.ModelType == typeof(object) &&
                modelOrDeclaredType != typeof(object))
            {
                // Base ModelMetadata on new type when there's no property information to preserve and type changes to
                // something besides typeof(object).
                ModelExplorer = _metadataProvider.GetModelExplorerForType(modelOrDeclaredType, model);
            }
            else if (!declaredModelType.IsAssignableFrom(source.ModelMetadata.ModelType))
            {
                // Base ModelMetadata on new type when existing metadata is incompatible with the new declared type.
                ModelExplorer = _metadataProvider.GetModelExplorerForType(modelOrDeclaredType, model);
            }
            else if (modelType != null && !source.ModelMetadata.ModelType.IsAssignableFrom(modelType))
            {
                // Base ModelMetadata on new type when new model is incompatible with the existing metadata.
                ModelExplorer = _metadataProvider.GetModelExplorerForType(modelType, model);
            }
            else if (object.ReferenceEquals(model, source.ModelExplorer.Model))
            {
                // Source's ModelExplorer is already exactly correct.
                ModelExplorer = source.ModelExplorer;
            }
            else
            {
                // The existing metadata is compatible with the value and declared type but it's a new value.
                ModelExplorer = new ModelExplorer(
                    _metadataProvider,
                    source.ModelExplorer.Container,
                    source.ModelMetadata,
                    model);
            }

            // Ensure the given Model is compatible with _declaredModelType. Do not do this one of the following
            // special cases:
            // - Constructing a ViewDataDictionary<TModel> where TModel is a non-Nullable value type. This may for
            // example occur when activating a RazorPage<int> and the container is null.
            // - Constructing a ViewDataDictionary<object> immediately before overwriting ModelExplorer with correct
            // information. See TemplateBuilder.Build().
            if (model != null)
            {
                EnsureCompatible(model);
            }
        }

        private ViewDataDictionary(
            IModelMetadataProvider metadataProvider,
            ModelStateDictionary modelState,
            Type declaredModelType,
            IDictionary<string, object> data,
            TemplateInfo templateInfo)
        {
            _metadataProvider = metadataProvider;
            ModelState = modelState;
            _declaredModelType = declaredModelType;
            _data = data;
            TemplateInfo = templateInfo;
        }

        /// <summary>
        /// Gets or sets the current model.
        /// </summary>
        public object Model
        {
            get
            {
                return ModelExplorer.Model;
            }
            set
            {
                // Reset ModelExplorer to ensure Model and ModelExplorer.Model remain equal.
                SetModel(value);
            }
        }

        /// <summary>
        /// Gets the <see cref="ModelStateDictionary"/>.
        /// </summary>
        public ModelStateDictionary ModelState { get; }

        /// <summary>
        /// Gets the <see cref="ModelBinding.ModelMetadata"/> for an expression, the <see cref="Model"/> (if
        /// non-<c>null</c>), or the declared <see cref="Type"/>.
        /// </summary>
        /// <remarks>
        /// Value is never <c>null</c> but may describe the <see cref="object"/> class in some cases. This may for
        /// example occur in controllers.
        /// </remarks>
        public ModelMetadata ModelMetadata
        {
            get
            {
                return ModelExplorer.Metadata;
            }
        }

        /// <summary>
        /// Gets or sets the <see cref="ViewFeatures.ModelExplorer"/> for the <see cref="Model"/>.
        /// </summary>
        public ModelExplorer ModelExplorer { get; set; }

        /// <summary>
        /// Gets the <see cref="ViewFeatures.TemplateInfo"/>.
        /// </summary>
        public TemplateInfo TemplateInfo { get; }

        #region IDictionary properties
        /// <inheritdoc />
        // Do not just pass through to _data: Indexer should not throw a KeyNotFoundException.
        public object this[string index]
        {
            get
            {
                object result;
                _data.TryGetValue(index, out result);
                return result;
            }
            set
            {
                _data[index] = value;
            }
        }

        /// <inheritdoc />
        public int Count
        {
            get { return _data.Count; }
        }

        /// <inheritdoc />
        public bool IsReadOnly
        {
            get { return _data.IsReadOnly; }
        }

        /// <inheritdoc />
        public ICollection<string> Keys
        {
            get { return _data.Keys; }
        }

        /// <inheritdoc />
        public ICollection<object> Values
        {
            get { return _data.Values; }
        }
        #endregion

        // for unit testing
        internal IDictionary<string, object> Data
        {
            get { return _data; }
        }

        /// <summary>
        /// Gets value of named <paramref name="expression"/> in this <see cref="ViewDataDictionary"/>.
        /// </summary>
        /// <param name="expression">Expression name, relative to the current model.</param>
        /// <returns>Value of named <paramref name="expression"/> in this <see cref="ViewDataDictionary"/>.</returns>
        /// <remarks>
        /// Looks up <paramref name="expression"/> in the dictionary first. Falls back to evaluating it against
        /// <see cref="Model"/>.
        /// </remarks>
        public object Eval(string expression)
        {
            var info = GetViewDataInfo(expression);
            return (info != null) ? info.Value : null;
        }

        /// <summary>
        /// Gets value of named <paramref name="expression"/> in this <see cref="ViewDataDictionary"/>, formatted
        /// using given <paramref name="format"/>.
        /// </summary>
        /// <param name="expression">Expression name, relative to the current model.</param>
        /// <param name="format">
        /// The composite format <see cref="string"/> (see http://msdn.microsoft.com/en-us/library/txafckwd.aspx).
        /// </param>
        /// <returns>
        /// Value of named <paramref name="expression"/> in this <see cref="ViewDataDictionary"/>, formatted using
        /// given <paramref name="format"/>.
        /// </returns>
        /// <remarks>
        /// Looks up <paramref name="expression"/> in the dictionary first. Falls back to evaluating it against
        /// <see cref="Model"/>.
        /// </remarks>
        public string Eval(string expression, string format)
        {
            var value = Eval(expression);
            return FormatValue(value, format);
        }

        /// <summary>
        /// Formats the given <paramref name="value"/> using given <paramref name="format"/>.
        /// </summary>
        /// <param name="value">The value to format.</param>
        /// <param name="format">
        /// The composite format <see cref="string"/> (see http://msdn.microsoft.com/en-us/library/txafckwd.aspx).
        /// </param>
        /// <returns>The formatted <see cref="string"/>.</returns>
        public static string FormatValue(object value, string format)
        {
            if (value == null)
            {
                return string.Empty;
            }

            if (string.IsNullOrEmpty(format))
            {
                return Convert.ToString(value, CultureInfo.CurrentCulture);
            }
            else
            {
                return string.Format(CultureInfo.CurrentCulture, format, value);
            }
        }

        /// <summary>
        /// Gets <see cref="ViewDataInfo"/> for named <paramref name="expression"/> in this
        /// <see cref="ViewDataDictionary"/>.
        /// </summary>
        /// <param name="expression">Expression name, relative to the current model.</param>
        /// <returns>
        /// <see cref="ViewDataInfo"/> for named <paramref name="expression"/> in this
        /// <see cref="ViewDataDictionary"/>.
        /// </returns>
        /// <remarks>
        /// Looks up <paramref name="expression"/> in the dictionary first. Falls back to evaluating it against
        /// <see cref="Model"/>.
        /// </remarks>
        public ViewDataInfo GetViewDataInfo(string expression)
        {
            return ViewDataEvaluator.Eval(this, expression);
        }

        /// <summary>
        /// Set <see cref="ModelExplorer"/> to ensure <see cref="Model"/> and <see cref="ModelExplorer.Model"/>
        /// reflect the new <paramref name="value"/>.
        /// </summary>
        /// <param name="value">New <see cref="Model"/> value.</param>
        protected virtual void SetModel(object value)
        {
            // Update ModelExplorer to reflect the new value. When possible, preserve ModelMetadata to avoid losing
            // property information.
            var modelType = value?.GetType();
            if (ModelMetadata.MetadataKind == ModelMetadataKind.Type &&
                ModelMetadata.ModelType == typeof(object) &&
                modelType != null &&
                modelType != typeof(object))
            {
                // Base ModelMetadata on new type when there's no property information to preserve and type changes to
                // something besides typeof(object).
                ModelExplorer = _metadataProvider.GetModelExplorerForType(modelType, value);
            }
            else if (modelType != null && !ModelMetadata.ModelType.IsAssignableFrom(modelType))
            {
                // Base ModelMetadata on new type when new model is incompatible with the existing metadata. The most
                // common case is _declaredModelType==typeof(object), metadata was copied from another VDD, and user
                // code sets the Model to a new type e.g. within a view component or a view that lacks an @model
                // directive.
                ModelExplorer = _metadataProvider.GetModelExplorerForType(modelType, value);
            }
            else if (object.ReferenceEquals(value, Model))
            {
                // The metadata matches and the model is literally the same; usually nothing to do here.
                if (value == null &&
                    !ModelMetadata.IsReferenceOrNullableType &&
                    _declaredModelType != ModelMetadata.ModelType)
                {
                    // Base ModelMetadata on declared type when setting Model to null, source VDD's Model was never
                    // set, and source VDD had a non-Nullable value type. Though _declaredModelType might also be a
                    // non-Nullable value type, would need to duplicate logic behind
                    // ModelMetadata.IsReferenceOrNullableType to avoid this allocation in the error case.
                    ModelExplorer = _metadataProvider.GetModelExplorerForType(_declaredModelType, value);
                }
            }
            else
            {
                // The existing metadata is compatible with the value but it's a new value.
                ModelExplorer = new ModelExplorer(_metadataProvider, ModelExplorer.Container, ModelMetadata, value);
            }

            EnsureCompatible(value);
        }

        // Throw if given value is incompatible with the declared Model Type.
        private void EnsureCompatible(object value)
        {
            // IsCompatibleObject verifies if the value is either an instance of _declaredModelType or (if value is
            // null) that _declaredModelType is a nullable type.
            var castWillSucceed = IsCompatibleWithDeclaredType(value);
            if (!castWillSucceed)
            {
                string message;
                if (value == null)
                {
                    message = Resources.FormatViewData_ModelCannotBeNull(_declaredModelType);
                }
                else
                {
                    message = Resources.FormatViewData_WrongTModelType(value.GetType(), _declaredModelType);
                }

                throw new InvalidOperationException(message);
            }
        }

        // Call after updating the ModelExplorer because this uses both _declaredModelType and ModelMetadata. May
        // otherwise get incorrect compatibility errors.
        private bool IsCompatibleWithDeclaredType(object value)
        {
            if (value == null)
            {
                // In this case ModelMetadata.ModelType matches _declaredModelType.
                return ModelMetadata.IsReferenceOrNullableType;
            }
            else
            {
                return _declaredModelType.IsAssignableFrom(value.GetType());
            }
        }

        #region IDictionary methods
        /// <inheritdoc />
        public void Add(string key, object value)
        {
            if (key == null)
            {
                throw new ArgumentNullException(nameof(key));
            }

            _data.Add(key, value);
        }

        /// <inheritdoc />
        public bool ContainsKey(string key)
        {
            if (key == null)
            {
                throw new ArgumentNullException(nameof(key));
            }

            return _data.ContainsKey(key);
        }

        /// <inheritdoc />
        public bool Remove(string key)
        {
            if (key == null)
            {
                throw new ArgumentNullException(nameof(key));
            }

            return _data.Remove(key);
        }

        /// <inheritdoc />
        public bool TryGetValue(string key, out object value)
        {
            if (key == null)
            {
                throw new ArgumentNullException(nameof(key));
            }

            return _data.TryGetValue(key, out value);
        }

        /// <inheritdoc />
        public void Add(KeyValuePair<string, object> item)
        {
            _data.Add(item);
        }

        /// <inheritdoc />
        public void Clear()
        {
            _data.Clear();
        }

        /// <inheritdoc />
        public bool Contains(KeyValuePair<string, object> item)
        {
            return _data.Contains(item);
        }

        /// <inheritdoc />
        public void CopyTo(KeyValuePair<string, object>[] array, int arrayIndex)
        {
            if (array == null)
            {
                throw new ArgumentNullException(nameof(array));
            }

            _data.CopyTo(array, arrayIndex);
        }

        /// <inheritdoc />
        public bool Remove(KeyValuePair<string, object> item)
        {
            return _data.Remove(item);
        }

        /// <inheritdoc />
        IEnumerator<KeyValuePair<string, object>> IEnumerable<KeyValuePair<string, object>>.GetEnumerator()
        {
            return _data.GetEnumerator();
        }

        /// <inheritdoc />
        IEnumerator IEnumerable.GetEnumerator()
        {
            return _data.GetEnumerator();
        }
        #endregion
    }
}