Add `ModelBindingContext.IsFirstChanceBinding` and `IsTopLevelObject`

- cleanup duplicate code now that #2445 is fixed
- update unit tests using old `ModelBindingContext` setups
- fix (just) one integration test where `MutableObjectModelBinder` incorrectly calculated
  `isTopLevelObject` and returned a non-`null` model
- undo temporary changes in `BodyModelBinderTests` due to increased reliance on incorrect
  `isTopLevelObject` in #2445 fix

nits:
- combine tests that are now duplicates
- beef up coverage of some `MutableObjectModelBinderTest` cases
- remove unused `using`s

src/Microsoft.AspNet.Mvc.Abstractions/ModelBinding/ModelBindingContext.cs

@@ -174,8 +174,31 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
         /// Gets or sets a value that indicates whether the binder should use an empty prefix to look up
         /// values in <see cref="IValueProvider"/> when no values are found using the <see cref="ModelName"/> prefix.
         /// </summary>
+        /// <remarks>
+        /// Passed into the model binding system. Should not be <c>true</c> when <see cref="IsTopLevelObject"/> is
+        /// <c>false</c>.
+        /// </remarks>
         public bool FallbackToEmptyPrefix { get; set; }
 
+        /// <summary>
+        /// Gets or sets an indication that the current binder is handling the top-level object.
+        /// </summary>
+        /// <remarks>Passed into the model binding system.</remarks>
+        public bool IsTopLevelObject { get; set; }
+
+        /// <summary>
+        /// Gets or sets an indication that the model binding system will make another binding attempt (e.g. fall back
+        /// to the empty prefix) after this one.
+        /// </summary>
+        /// <remarks>
+        /// Not passed into the model binding system but instead set by the top-level binder. With built-in binders,
+        /// <c>true</c> only in binders called directly from a
+        /// <c>Microsoft.AspNet.Mvc.ModelBinding.CompositeModelBinder</c> that was passed a
+        /// <see cref="ModelBindingContext"/> with <see cref="FallbackToEmptyPrefix"/> <c>true</c>. <c>false</c>
+        /// otherwise.
+        /// </remarks>
+        public bool IsFirstChanceBinding { get; set; }
+
         /// <summary>
         /// Gets or sets the <see cref="IValueProvider"/> associated with this context.
         /// </summary>

src/Microsoft.AspNet.Mvc.Core/DefaultControllerActionArgumentBinder.cs

@@ -196,6 +196,7 @@ namespace Microsoft.AspNet.Mvc
                 bindingInfo,
                 parameterName);
 
+            modelBindingContext.IsTopLevelObject = true;
             modelBindingContext.ModelState = modelState;
             modelBindingContext.ValueProvider = operationBindingContext.ValueProvider;
             modelBindingContext.OperationBindingContext = operationBindingContext;

src/Microsoft.AspNet.Mvc.Core/ModelBinding/BodyModelBinder.cs

@@ -30,8 +30,7 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
             // For compatibility with MVC 5.0 for top level object we want to consider an empty key instead of
             // the parameter name/a custom name. In all other cases (like when binding body to a property) we
             // consider the entire ModelName as a prefix.
-            var isTopLevelObject = bindingContext.ModelMetadata.ContainerType == null;
+            var modelBindingKey = bindingContext.IsTopLevelObject ? string.Empty : bindingContext.ModelName;
-            var modelBindingKey = isTopLevelObject ? string.Empty : bindingContext.ModelName;
 
             var httpContext = bindingContext.OperationBindingContext.HttpContext;
 

src/Microsoft.AspNet.Mvc.Core/ModelBinding/CollectionModelBinder.cs

@@ -27,12 +27,9 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
 
             if (!await bindingContext.ValueProvider.ContainsPrefixAsync(bindingContext.ModelName))
             {
-                // If this is the fallback case, and we failed to find data as a top-level model, then generate a
+                // If this is the fallback case and we failed to find data for a top-level model, then generate a
                 // default 'empty' model and return it.
-                var isTopLevelObject = bindingContext.ModelMetadata.ContainerType == null;
+                if (!bindingContext.IsFirstChanceBinding && bindingContext.IsTopLevelObject)
-                var hasExplicitAlias = bindingContext.BinderModelName != null;
-
-                if (isTopLevelObject && (hasExplicitAlias || bindingContext.ModelName == string.Empty))
                 {
                     model = CreateEmptyCollection();
 

src/Microsoft.AspNet.Mvc.Core/ModelBinding/CompositeModelBinder.cs

@@ -34,12 +34,15 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
 
         public virtual async Task<ModelBindingResult> BindModelAsync([NotNull] ModelBindingContext bindingContext)
         {
+            // Will there be a last chance (fallback) binding attempt?
+            var isFirstChanceBinding = bindingContext.FallbackToEmptyPrefix &&
+                !string.IsNullOrEmpty(bindingContext.ModelName);
+
             var newBindingContext = CreateNewBindingContext(bindingContext, bindingContext.ModelName);
+            newBindingContext.IsFirstChanceBinding = isFirstChanceBinding;
             var modelBindingResult = await TryBind(newBindingContext);
 
-            if (modelBindingResult == null &&
+            if (modelBindingResult == null && isFirstChanceBinding)
-                bindingContext.FallbackToEmptyPrefix &&
-                !string.IsNullOrEmpty(bindingContext.ModelName))
             {
                 // Fall back to empty prefix.
                 newBindingContext = CreateNewBindingContext(bindingContext, modelName: string.Empty);
@@ -142,6 +145,7 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
                 BinderModelName = oldBindingContext.BinderModelName,
                 BindingSource = oldBindingContext.BindingSource,
                 BinderType = oldBindingContext.BinderType,
+                IsTopLevelObject = oldBindingContext.IsTopLevelObject,
             };
 
             newBindingContext.OperationBindingContext.BodyBindingState = GetBodyBindingState(oldBindingContext);

src/Microsoft.AspNet.Mvc.Core/ModelBinding/KeyValuePairModelBinder.cs

@@ -62,12 +62,9 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
             }
             else
             {
-                // If this is the fallback case, and we failed to find data as a top-level model, then generate a
+                // If this is the fallback case and we failed to find data for a top-level model, then generate a
                 // default 'empty' model and return it.
-                var isTopLevelObject = bindingContext.ModelMetadata.ContainerType == null;
+                if (!bindingContext.IsFirstChanceBinding && bindingContext.IsTopLevelObject)
-                var hasExplicitAlias = bindingContext.BinderModelName != null;
-
-                if (isTopLevelObject && (hasExplicitAlias || bindingContext.ModelName == string.Empty))
                 {
                     var model = new KeyValuePair<TKey, TValue>();
 

src/Microsoft.AspNet.Mvc.Core/ModelBinding/MutableObjectModelBinder.cs

@@ -71,9 +71,7 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
         internal async Task<bool> CanCreateModel(MutableObjectBinderContext context)
         {
             var bindingContext = context.ModelBindingContext;
-
+            var isTopLevelObject = bindingContext.IsTopLevelObject;
-            var isTopLevelObject = bindingContext.ModelMetadata.ContainerType == null;
-            var hasExplicitAlias = bindingContext.BinderModelName != null;
 
             // If we get here the model is a complex object which was not directly bound by any previous model binder,
             // so we want to decide if we want to continue binding. This is important to get right to avoid infinite
@@ -83,34 +81,24 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
             // will always include value provider data. For instance if the model is marked with [FromBody], then we
             // can just skip it. A greedy source cannot be a value provider.
             //
-            // If the model isn't marked with ANY binding source, then we assume it's ok also.
+            // If the model isn't marked with ANY binding source, then we assume it's OK also.
             //
             // We skip this check if it is a top level object because we want to always evaluate
             // the creation of top level object (this is also required for ModelBinderAttribute to work.)
             var bindingSource = bindingContext.BindingSource;
-            if (!isTopLevelObject &&
+            if (!isTopLevelObject && bindingSource != null && bindingSource.IsGreedy)
-                bindingSource != null &&
-                bindingSource.IsGreedy)
             {
                 return false;
             }
 
-            // Create the object if :
+            // Create the object if:
-            // 1. It is a top level model with an explicit user supplied prefix.
+            // 1. It is a top level model and no later fallback (to empty prefix) will occur.
-            //    In this case since it will never fallback to empty prefix, we need to create the model here.
+            if (isTopLevelObject && !bindingContext.IsFirstChanceBinding)
-            if (isTopLevelObject && hasExplicitAlias)
             {
                 return true;
             }
 
-            // 2. It is a top level object and there is no model name ( Fallback to empty prefix case ).
+            // 2. Any of the model properties can be bound using a value provider.
-            //    This is necessary as we do not want to depend on a value provider to contain an empty prefix.
-            if (isTopLevelObject && bindingContext.ModelName == string.Empty)
-            {
-                return true;
-            }
-
-            // 3. Any of the model properties can be bound using a value provider.
             if (await CanValueBindAnyModelProperties(context))
             {
                 return true;

src/Microsoft.AspNet.Mvc.Core/ModelBindingHelper.cs

@@ -2,10 +2,7 @@
 // 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.Diagnostics;
-using System.Globalization;
 using System.Linq;
 using System.Linq.Expressions;
 using System.Reflection;
@@ -303,8 +300,9 @@ namespace Microsoft.AspNet.Mvc
                 ModelState = modelState,
                 ValueProvider = valueProvider,
                 FallbackToEmptyPrefix = true,
+                IsTopLevelObject = true,
                 OperationBindingContext = operationBindingContext,
-                PropertyFilter = predicate
+                PropertyFilter = predicate,
             };
 
             var modelBindingResult = await modelBinder.BindModelAsync(modelBindingContext);

test/Microsoft.AspNet.Mvc.Core.Test/ModelBinding/ArrayModelBinderTest.cs

@@ -37,13 +37,18 @@ namespace Microsoft.AspNet.Mvc.ModelBinding.Test
         }
 
         [Fact]
-        public async Task ArrayModelBinder_DoesNotCreateCollection_ForTopLevelModel_OnFirstPass()
+        public async Task ArrayModelBinder_DoesNotCreateCollection_IfIsTopLevelObjectAndIsFirstChanceBinding()
         {
             // Arrange
             var binder = new ArrayModelBinder<string>();
 
             var context = CreateContext();
-            context.ModelName = "param";
+            context.IsFirstChanceBinding = true;
+            context.IsTopLevelObject = true;
+
+            // Explicit prefix and empty model name both ignored.
+            context.BinderModelName = "prefix";
+            context.ModelName = string.Empty;
 
             var metadataProvider = context.OperationBindingContext.MetadataProvider;
             context.ModelMetadata = metadataProvider.GetMetadataForType(typeof(string[]));
@@ -58,13 +63,16 @@ namespace Microsoft.AspNet.Mvc.ModelBinding.Test
         }
 
         [Fact]
-        public async Task ArrayModelBinder_CreatesEmptyCollection_ForTopLevelModel_OnFallback()
+        public async Task ArrayModelBinder_CreatesEmptyCollection_IfIsTopLevelObjectAndNotIsFirstChanceBinding()
         {
             // Arrange
             var binder = new ArrayModelBinder<string>();
 
             var context = CreateContext();
-            context.ModelName = string.Empty;
+            context.IsTopLevelObject = true;
+
+            // Lack of prefix and non-empty model name both ignored.
+            context.ModelName = "modelName";
 
             var metadataProvider = context.OperationBindingContext.MetadataProvider;
             context.ModelMetadata = metadataProvider.GetMetadataForType(typeof(string[]));
@@ -78,37 +86,7 @@ namespace Microsoft.AspNet.Mvc.ModelBinding.Test
             Assert.NotNull(result);
 
             Assert.Empty(Assert.IsType<string[]>(result.Model));
-            Assert.Equal(string.Empty, result.Key);
+            Assert.Equal("modelName", result.Key);
-            Assert.True(result.IsModelSet);
-
-            Assert.Same(result.ValidationNode.Model, result.Model);
-            Assert.Same(result.ValidationNode.Key, result.Key);
-            Assert.Same(result.ValidationNode.ModelMetadata, context.ModelMetadata);
-        }
-
-        [Fact]
-        public async Task ArrayModelBinder_CreatesEmptyCollection_ForTopLevelModel_WithExplicitPrefix()
-        {
-            // Arrange
-            var binder = new ArrayModelBinder<string>();
-
-            var context = CreateContext();
-            context.ModelName = "prefix";
-            context.BinderModelName = "prefix";
-
-            var metadataProvider = context.OperationBindingContext.MetadataProvider;
-            context.ModelMetadata = metadataProvider.GetMetadataForType(typeof(string[]));
-
-            context.ValueProvider = new TestValueProvider(new Dictionary<string, object>());
-
-            // Act
-            var result = await binder.BindModelAsync(context);
-
-            // Assert
-            Assert.NotNull(result);
-
-            Assert.Empty(Assert.IsType<string[]>(result.Model));
-            Assert.Equal("prefix", result.Key);
             Assert.True(result.IsModelSet);
 
             Assert.Same(result.ValidationNode.Model, result.Model);
@@ -119,7 +97,7 @@ namespace Microsoft.AspNet.Mvc.ModelBinding.Test
         [Theory]
         [InlineData("")]
         [InlineData("param")]
-        public async Task ArrayModelBinder_DoesNotCreateCollection_ForNonTopLevelModel(string prefix)
+        public async Task ArrayModelBinder_DoesNotCreateCollection_IfNotIsTopLevelObject(string prefix)
         {
             // Arrange
             var binder = new ArrayModelBinder<string>();

test/Microsoft.AspNet.Mvc.Core.Test/ModelBinding/BodyModelBinderTests.cs

@@ -10,7 +10,6 @@ using System.Threading.Tasks;
 using Microsoft.AspNet.Http;
 using Microsoft.AspNet.Http.Internal;
 using Microsoft.AspNet.Routing;
-using Microsoft.Framework.DependencyInjection;
 using Microsoft.Net.Http.Headers;
 using Moq;
 using Xunit;
@@ -279,6 +278,7 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
 
             var bindingContext = new ModelBindingContext
             {
+                IsTopLevelObject = true,
                 ModelMetadata = metadataProvider.GetMetadataForType(modelType),
                 ModelName = "someName",
                 ValueProvider = Mock.Of<IValueProvider>(),

test/Microsoft.AspNet.Mvc.Core.Test/ModelBinding/CollectionModelBinderTest.cs

@@ -218,13 +218,18 @@ namespace Microsoft.AspNet.Mvc.ModelBinding.Test
         }
 
         [Fact]
-        public async Task CollectionModelBinder_DoesNotCreateCollection_ForTopLevelModel_OnFirstPass()
+        public async Task CollectionModelBinder_DoesNotCreateCollection_IfIsTopLevelObjectAndIsFirstChanceBinding()
         {
             // Arrange
             var binder = new CollectionModelBinder<string>();
 
             var context = CreateContext();
-            context.ModelName = "param";
+            context.IsTopLevelObject = true;
+            context.IsFirstChanceBinding = true;
+
+            // Explicit prefix and empty model name both ignored.
+            context.BinderModelName = "prefix";
+            context.ModelName = string.Empty;
 
             var metadataProvider = context.OperationBindingContext.MetadataProvider;
             context.ModelMetadata = metadataProvider.GetMetadataForType(typeof(List<string>));
@@ -239,13 +244,16 @@ namespace Microsoft.AspNet.Mvc.ModelBinding.Test
         }
 
         [Fact]
-        public async Task CollectionModelBinder_CreatesEmptyCollection_ForTopLevelModel_OnFallback()
+        public async Task CollectionModelBinder_CreatesEmptyCollection_IfIsTopLevelObjectAndNotIsFirstChanceBinding()
         {
             // Arrange
             var binder = new CollectionModelBinder<string>();
 
             var context = CreateContext();
-            context.ModelName = string.Empty;
+            context.IsTopLevelObject = true;
+
+            // Lack of prefix and non-empty model name both ignored.
+            context.ModelName = "modelName";
 
             var metadataProvider = context.OperationBindingContext.MetadataProvider;
             context.ModelMetadata = metadataProvider.GetMetadataForType(typeof(List<string>));
@@ -259,37 +267,7 @@ namespace Microsoft.AspNet.Mvc.ModelBinding.Test
             Assert.NotNull(result);
 
             Assert.Empty(Assert.IsType<List<string>>(result.Model));
-            Assert.Equal(string.Empty, result.Key);
+            Assert.Equal("modelName", result.Key);
-            Assert.True(result.IsModelSet);
-
-            Assert.Same(result.ValidationNode.Model, result.Model);
-            Assert.Same(result.ValidationNode.Key, result.Key);
-            Assert.Same(result.ValidationNode.ModelMetadata, context.ModelMetadata);
-        }
-
-        [Fact]
-        public async Task CollectionModelBinder_CreatesEmptyCollection_ForTopLevelModel_WithExplicitPrefix()
-        {
-            // Arrange
-            var binder = new CollectionModelBinder<string>();
-
-            var context = CreateContext();
-            context.ModelName = "prefix";
-            context.BinderModelName = "prefix";
-
-            var metadataProvider = context.OperationBindingContext.MetadataProvider;
-            context.ModelMetadata = metadataProvider.GetMetadataForType(typeof(List<string>));
-
-            context.ValueProvider = new TestValueProvider(new Dictionary<string, object>());
-
-            // Act
-            var result = await binder.BindModelAsync(context);
-
-            // Assert
-            Assert.NotNull(result);
-
-            Assert.Empty(Assert.IsType<List<string>>(result.Model));
-            Assert.Equal("prefix", result.Key);
             Assert.True(result.IsModelSet);
 
             Assert.Same(result.ValidationNode.Model, result.Model);
@@ -300,7 +278,7 @@ namespace Microsoft.AspNet.Mvc.ModelBinding.Test
         [Theory]
         [InlineData("")]
         [InlineData("param")]
-        public async Task CollectionModelBinder_DoesNotCreateCollection_ForNonTopLevelModel(string prefix)
+        public async Task CollectionModelBinder_DoesNotCreateCollection_IfNotIsTopLevelObject(string prefix)
         {
             // Arrange
             var binder = new CollectionModelBinder<string>();

test/Microsoft.AspNet.Mvc.Core.Test/ModelBinding/DictionaryModelBinderTest.cs

@@ -65,13 +65,18 @@ namespace Microsoft.AspNet.Mvc.ModelBinding.Test
         }
 
         [Fact]
-        public async Task DictionaryModelBinder_DoesNotCreateCollection_ForTopLevelModel_OnFirstPass()
+        public async Task DictionaryModelBinder_DoesNotCreateCollection_IfIsTopLevelObjectAndIsFirstChanceBinding()
         {
             // Arrange
             var binder = new DictionaryModelBinder<string, string>();
 
             var context = CreateContext();
-            context.ModelName = "param";
+            context.IsTopLevelObject = true;
+            context.IsFirstChanceBinding = true;
+
+            // Explicit prefix and empty model name both ignored.
+            context.BinderModelName = "prefix";
+            context.ModelName = string.Empty;
 
             var metadataProvider = context.OperationBindingContext.MetadataProvider;
             context.ModelMetadata = metadataProvider.GetMetadataForType(typeof(Dictionary<string, string>));
@@ -86,13 +91,16 @@ namespace Microsoft.AspNet.Mvc.ModelBinding.Test
         }
 
         [Fact]
-        public async Task DictionaryModelBinder_CreatesEmptyCollection_ForTopLevelModel_OnFallback()
+        public async Task DictionaryModelBinder_CreatesEmptyCollection_IfIsTopLevelObjectAndNotIsFirstChanceBinding()
         {
             // Arrange
             var binder = new DictionaryModelBinder<string, string>();
 
             var context = CreateContext();
-            context.ModelName = string.Empty;
+            context.IsTopLevelObject = true;
+
+            // Lack of prefix and non-empty model name both ignored.
+            context.ModelName = "modelName";
 
             var metadataProvider = context.OperationBindingContext.MetadataProvider;
             context.ModelMetadata = metadataProvider.GetMetadataForType(typeof(Dictionary<string, string>));
@@ -106,37 +114,7 @@ namespace Microsoft.AspNet.Mvc.ModelBinding.Test
             Assert.NotNull(result);
 
             Assert.Empty(Assert.IsType<Dictionary<string, string>>(result.Model));
-            Assert.Equal(string.Empty, result.Key);
+            Assert.Equal("modelName", result.Key);
-            Assert.True(result.IsModelSet);
-
-            Assert.Same(result.ValidationNode.Model, result.Model);
-            Assert.Same(result.ValidationNode.Key, result.Key);
-            Assert.Same(result.ValidationNode.ModelMetadata, context.ModelMetadata);
-        }
-
-        [Fact]
-        public async Task DictionaryModelBinder_CreatesEmptyCollection_ForTopLevelModel_WithExplicitPrefix()
-        {
-            // Arrange
-            var binder = new DictionaryModelBinder<string, string>();
-
-            var context = CreateContext();
-            context.ModelName = "prefix";
-            context.BinderModelName = "prefix";
-
-            var metadataProvider = context.OperationBindingContext.MetadataProvider;
-            context.ModelMetadata = metadataProvider.GetMetadataForType(typeof(Dictionary<string, string>));
-
-            context.ValueProvider = new TestValueProvider(new Dictionary<string, object>());
-
-            // Act
-            var result = await binder.BindModelAsync(context);
-
-            // Assert
-            Assert.NotNull(result);
-
-            Assert.Empty(Assert.IsType<Dictionary<string, string>>(result.Model));
-            Assert.Equal("prefix", result.Key);
             Assert.True(result.IsModelSet);
 
             Assert.Same(result.ValidationNode.Model, result.Model);
@@ -147,7 +125,7 @@ namespace Microsoft.AspNet.Mvc.ModelBinding.Test
         [Theory]
         [InlineData("")]
         [InlineData("param")]
-        public async Task DictionaryModelBinder_DoesNotCreateCollection_ForNonTopLevelModel(string prefix)
+        public async Task DictionaryModelBinder_DoesNotCreateCollection_IfNotIsTopLevelObject(string prefix)
         {
             // Arrange
             var binder = new DictionaryModelBinder<string, string>();

test/Microsoft.AspNet.Mvc.Core.Test/ModelBinding/KeyValuePairModelBinderTest.cs

@@ -148,13 +148,18 @@ namespace Microsoft.AspNet.Mvc.ModelBinding.Test
         }
 
         [Fact]
-        public async Task KeyValuePairModelBinder_DoesNotCreateCollection_ForTopLevelModel_OnFirstPass()
+        public async Task KeyValuePairModelBinder_DoesNotCreateCollection_IfIsTopLevelObjectAndIsFirstChanceBinding()
         {
             // Arrange
             var binder = new KeyValuePairModelBinder<string, string>();
 
             var context = CreateContext();
-            context.ModelName = "param";
+            context.IsTopLevelObject = true;
+            context.IsFirstChanceBinding = true;
+
+            // Explicit prefix and empty model name both ignored.
+            context.BinderModelName = "prefix";
+            context.ModelName = string.Empty;
 
             var metadataProvider = context.OperationBindingContext.MetadataProvider;
             context.ModelMetadata = metadataProvider.GetMetadataForType(typeof(KeyValuePair<string, string>));
@@ -169,13 +174,16 @@ namespace Microsoft.AspNet.Mvc.ModelBinding.Test
         }
 
         [Fact]
-        public async Task KeyValuePairModelBinder_CreatesEmptyCollection_ForTopLevelModel_OnFallback()
+        public async Task KeyValuePairModelBinder_CreatesEmptyCollection_IfIsTopLevelObjectAndNotIsFirstChanceBinding()
         {
             // Arrange
             var binder = new KeyValuePairModelBinder<string, string>();
 
             var context = CreateContext();
-            context.ModelName = string.Empty;
+            context.IsTopLevelObject = true;
+
+            // Lack of prefix and non-empty model name both ignored.
+            context.ModelName = "modelName";
 
             var metadataProvider = context.OperationBindingContext.MetadataProvider;
             context.ModelMetadata = metadataProvider.GetMetadataForType(typeof(KeyValuePair<string, string>));
@@ -189,37 +197,7 @@ namespace Microsoft.AspNet.Mvc.ModelBinding.Test
             Assert.NotNull(result);
 
             Assert.Equal(default(KeyValuePair<string, string>), Assert.IsType<KeyValuePair<string, string>>(result.Model));
-            Assert.Equal(string.Empty, result.Key);
+            Assert.Equal("modelName", result.Key);
-            Assert.True(result.IsModelSet);
-
-            Assert.Equal(result.ValidationNode.Model, result.Model);
-            Assert.Same(result.ValidationNode.Key, result.Key);
-            Assert.Same(result.ValidationNode.ModelMetadata, context.ModelMetadata);
-        }
-
-        [Fact]
-        public async Task KeyValuePairModelBinder_CreatesEmptyCollection_ForTopLevelModel_WithExplicitPrefix()
-        {
-            // Arrange
-            var binder = new KeyValuePairModelBinder<string, string>();
-
-            var context = CreateContext();
-            context.ModelName = "prefix";
-            context.BinderModelName = "prefix";
-
-            var metadataProvider = context.OperationBindingContext.MetadataProvider;
-            context.ModelMetadata = metadataProvider.GetMetadataForType(typeof(KeyValuePair<string, string>));
-
-            context.ValueProvider = new TestValueProvider(new Dictionary<string, object>());
-
-            // Act
-            var result = await binder.BindModelAsync(context);
-
-            // Assert
-            Assert.NotNull(result);
-
-            Assert.Equal(default(KeyValuePair<string, string>), Assert.IsType<KeyValuePair<string, string>>(result.Model));
-            Assert.Equal("prefix", result.Key);
             Assert.True(result.IsModelSet);
 
             Assert.Equal(result.ValidationNode.Model, result.Model);
@@ -230,7 +208,7 @@ namespace Microsoft.AspNet.Mvc.ModelBinding.Test
         [Theory]
         [InlineData("")]
         [InlineData("param")]
-        public async Task KeyValuePairModelBinder_DoesNotCreateCollection_ForNonTopLevelModel(string prefix)
+        public async Task KeyValuePairModelBinder_DoesNotCreateCollection_IfNotIsTopLevelObject(string prefix)
         {
             // Arrange
             var binder = new KeyValuePairModelBinder<string, string>();

test/Microsoft.AspNet.Mvc.Core.Test/ModelBinding/MutableObjectModelBinderTest.cs

@@ -20,23 +20,42 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
     public class MutableObjectModelBinderTest
     {
         [Theory]
-        [InlineData(typeof(Person), true)]
+        [InlineData(true, true, "", "", false)]
-        [InlineData(typeof(Person), false)]
+        [InlineData(true, false, "", "", true)]
-        [InlineData(typeof(EmptyModel), true)]
+        [InlineData(false, true, "", "", false)] // !isTopLevelObject && isFirstChanceBinding cases are unexpected
-        [InlineData(typeof(EmptyModel), false)]
+        [InlineData(false, false, "", "", false)]
-        public async Task CanCreateModel_CreatesModel_ForTopLevelObjectIfThereIsExplicitPrefix(
+        [InlineData(true, true, "prefix", "", false)]
-            Type modelType,
+        [InlineData(true, false, "prefix", "", true)]
-            bool isPrefixProvided)
+        [InlineData(false, true, "prefix", "", false)]
+        [InlineData(false, false, "prefix", "", false)]
+        [InlineData(true, true, "", "dummyModelName", false)]
+        [InlineData(true, false, "", "dummyModelName", true)]
+        [InlineData(false, true, "", "dummyModelName", false)]
+        [InlineData(false, false, "", "dummyModelName", false)]
+        [InlineData(true, true, "prefix", "dummyModelName", false)]
+        [InlineData(true, false, "prefix", "dummyModelName", true)]
+        [InlineData(false, true, "prefix", "dummyModelName", false)]
+        [InlineData(false, false, "prefix", "dummyModelName", false)]
+        public async Task CanCreateModel_ReturnsTrue_IfIsTopLevelObjectAndNotIsFirstChanceBinding(
+            bool isTopLevelObject,
+            bool isFirstChanceBinding,
+            string binderModelName,
+            string modelName,
+            bool expectedCanCreate)
         {
             var mockValueProvider = new Mock<IValueProvider>();
-            mockValueProvider.Setup(o => o.ContainsPrefixAsync(It.IsAny<string>()))
+            mockValueProvider
-                             .Returns(Task.FromResult(false));
+                .Setup(o => o.ContainsPrefixAsync(It.IsAny<string>()))
+                .Returns(Task.FromResult(false));
 
             var metadataProvider = new TestModelMetadataProvider();
             var bindingContext = new MutableObjectBinderContext
             {
                 ModelBindingContext = new ModelBindingContext
                 {
+                    IsTopLevelObject = isTopLevelObject,
+                    IsFirstChanceBinding = isFirstChanceBinding,
+
                     // Random type.
                     ModelMetadata = metadataProvider.GetMetadataForType(typeof(Person)),
                     ValueProvider = mockValueProvider.Object,
@@ -47,65 +66,25 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
                         ValidatorProvider = Mock.Of<IModelValidatorProvider>(),
                     },
 
-                    // Setting it to empty ensures that model does not get created becasue of no model name.
+                    // CanCreateModel() ignores the BinderModelName and ModelName properties.
-                    ModelName = "dummyModelName",
+                    BinderModelName = binderModelName,
-                    BinderModelName = isPrefixProvided ? "prefix" : null,
+                    ModelName = modelName,
-                }
+                },
             };
 
             var mutableBinder = new TestableMutableObjectModelBinder();
             bindingContext.PropertyMetadata = mutableBinder.GetMetadataForProperties(
-                                                                bindingContext.ModelBindingContext);
+                bindingContext.ModelBindingContext);
 
             // Act
-            var retModel = await mutableBinder.CanCreateModel(bindingContext);
+            var canCreate = await mutableBinder.CanCreateModel(bindingContext);
 
             // Assert
-            Assert.Equal(isPrefixProvided, retModel);
+            Assert.Equal(expectedCanCreate, canCreate);
-        }
-
-        [Theory]
-        [InlineData(typeof(Person), true)]
-        [InlineData(typeof(Person), false)]
-        [InlineData(typeof(EmptyModel), true)]
-        [InlineData(typeof(EmptyModel), false)]
-        public async Task
-            CanCreateModel_CreatesModel_ForTopLevelObjectIfThereIsEmptyModelName(Type modelType, bool emptyModelName)
-        {
-            var mockValueProvider = new Mock<IValueProvider>();
-            mockValueProvider.Setup(o => o.ContainsPrefixAsync(It.IsAny<string>()))
-                             .Returns(Task.FromResult(false));
-
-            var bindingContext = new MutableObjectBinderContext
-            {
-                ModelBindingContext = new ModelBindingContext
-                {
-                    // Random type.
-                    ModelMetadata = GetMetadataForType(typeof(Person)),
-                    ValueProvider = mockValueProvider.Object,
-                    OperationBindingContext = new OperationBindingContext
-                    {
-                        ValidatorProvider = Mock.Of<IModelValidatorProvider>(),
-                        ValueProvider = mockValueProvider.Object,
-                        MetadataProvider = TestModelMetadataProvider.CreateDefaultProvider()
-                    }
-                }
-            };
-
-            bindingContext.ModelBindingContext.ModelName = emptyModelName ? string.Empty : "dummyModelName";
-            var mutableBinder = new TestableMutableObjectModelBinder();
-            bindingContext.PropertyMetadata = mutableBinder.GetMetadataForProperties(
-                                                                bindingContext.ModelBindingContext);
-
-            // Act
-            var retModel = await mutableBinder.CanCreateModel(bindingContext);
-
-            // Assert
-            Assert.Equal(emptyModelName, retModel);
         }
 
         [Fact]
-        public async Task CanCreateModel_ReturnsFalse_ForNonTopLevelModel_IfModelIsMarkedWithBinderMetadata()
+        public async Task CanCreateModel_ReturnsFalse_IfNotIsTopLevelObjectAndModelIsMarkedWithBinderMetadata()
         {
             // Get the property metadata so that it is not a top level object.
             var modelMetadata = GetMetadataForType(typeof(Document))
@@ -135,13 +114,15 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
         }
 
         [Fact]
-        public async Task CanCreateModel_ReturnsTrue_ForTopLevelModel_IfModelIsMarkedWithBinderMetadata()
+        public async Task CanCreateModel_ReturnsTrue_IfIsTopLevelObjectAndModelIsMarkedWithBinderMetadata()
         {
             var bindingContext = new MutableObjectBinderContext
             {
                 ModelBindingContext = new ModelBindingContext
                 {
                     // Here the metadata represents a top level object.
+                    IsTopLevelObject = true,
+
                     ModelMetadata = GetMetadataForType(typeof(Document)),
                     OperationBindingContext = new OperationBindingContext
                     {
@@ -198,7 +179,8 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
         [Theory]
         [InlineData(true)]
         [InlineData(false)]
-        public async Task CanCreateModel_ReturnsTrue_ForNonTopLevelModel_BasedOnValueAvailability(bool valueAvailable)
+        public async Task CanCreateModel_ReturnsTrue_IfNotIsTopLevelObject_BasedOnValueAvailability(
+            bool valueAvailable)
         {
             // Arrange
             var mockValueProvider = new Mock<IValueProvider>(MockBehavior.Strict);
@@ -434,7 +416,7 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
         }
 
         [Fact]
-        public async Task BindModel_InitsInstance_ForEmptyModelName()
+        public async Task BindModel_InitsInstance_IfIsTopLevelObjectAndNotIsFirstChanceBinding()
         {
             // Arrange
             var mockValueProvider = new Mock<IValueProvider>();
@@ -444,6 +426,7 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
             var mockDtoBinder = new Mock<IModelBinder>();
             var bindingContext = new ModelBindingContext
             {
+                IsTopLevelObject = true,
                 ModelMetadata = GetMetadataForType(typeof(Person)),
                 ModelName = "",
                 ValueProvider = mockValueProvider.Object,

test/Microsoft.AspNet.Mvc.Extensions.Test/Rendering/DefaultHtmlGeneratorTest.cs

@@ -3,7 +3,6 @@
 
 using System;
 using System.Collections.Generic;
-using System.Globalization;
 using System.IO;
 using System.Linq;
 using Microsoft.AspNet.DataProtection;

test/Microsoft.AspNet.Mvc.IntegrationTests/GenericModelBinderIntegrationTest.cs

@@ -181,10 +181,9 @@ namespace Microsoft.AspNet.Mvc.IntegrationTests
             };
 
             // Need to have a key here so that the GenericModelBinder will recurse to bind elements.
-            var operationContext = ModelBindingTestHelper.GetOperationBindingContext(request =>
+            var operationContext = ModelBindingTestHelper.GetOperationBindingContext(
-            {
+                request => request.QueryString = new QueryString("?parameter.index=0"),
-                request.QueryString = new QueryString("?parameter.index=0");
+                options => options.ModelBinders.Add(new AddressBinder()));
-            });
 
             var modelState = new ModelStateDictionary();
 
@@ -204,6 +203,41 @@ namespace Microsoft.AspNet.Mvc.IntegrationTests
             Assert.True(modelState.IsValid);
         }
 
+        // Similar to the GenericModelBinder_BindsCollection_ElementTypeUsesGreedyModelBinder_WithPrefix_Success
+        // scenario but mis-configured. Model using a BindingSource for which no ModelBinder is enabled.
+        [Fact]
+        public async Task GenericModelBinder_BindsCollection_ElementTypeUsesGreedyBindingSource_WithPrefix_NullElement()
+        {
+            // Arrange
+            var argumentBinder = ModelBindingTestHelper.GetArgumentBinder();
+            var parameter = new ParameterDescriptor()
+            {
+                Name = "parameter",
+                ParameterType = typeof(Address[])
+            };
+
+            // Need to have a key here so that the GenericModelBinder will recurse to bind elements.
+            var operationContext = ModelBindingTestHelper.GetOperationBindingContext(
+                request => request.QueryString = new QueryString("?parameter.index=0"));
+
+            var modelState = new ModelStateDictionary();
+
+            // Act
+            var modelBindingResult = await argumentBinder.BindModelAsync(parameter, modelState, operationContext);
+
+            // Assert
+            Assert.NotNull(modelBindingResult);
+            Assert.True(modelBindingResult.IsModelSet);
+
+            var model = Assert.IsType<Address[]>(modelBindingResult.Model);
+            Assert.Equal(1, model.Length);
+            Assert.Null(model[0]);
+
+            Assert.Equal(0, modelState.Count);
+            Assert.Equal(0, modelState.ErrorCount);
+            Assert.True(modelState.IsValid);
+        }
+
         // This is part of a random sampling of scenarios where a GenericModelBinder is used
         // recursively.
         [Fact]

test/Microsoft.AspNet.Mvc.IntegrationTests/ValidationIntegrationTests.cs

@@ -4,7 +4,6 @@
 using System.Collections.Generic;
 using System.ComponentModel.DataAnnotations;
 using System.IO;
-using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
 using Microsoft.AspNet.Http;