Introducing ModelBinderFactory

This change separates model binding into IModelBinderProvider (decides
which binder to use) and IModelBinder (does binding). The
IModelBinderFactory is a new services with coordinates the creation of
model binders.

src/Microsoft.AspNetCore.Mvc.Abstractions/ModelBinding/IModelBinderProvider.cs

@@ -0,0 +1,19 @@
+// 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.
+
+namespace Microsoft.AspNetCore.Mvc.ModelBinding
+{
+    /// <summary>
+    /// Creates <see cref="IModelBinder"/> instances. Register <see cref="IModelBinderProvider"/>
+    /// instances in <c>MvcOptions</c>.
+    /// </summary>
+    public interface IModelBinderProvider
+    {
+        /// <summary>
+        /// Creates a <see cref="IModelBinder"/> based on <see cref="ModelBinderProviderContext"/>.
+        /// </summary>
+        /// <param name="context">The <see cref="ModelBinderProviderContext"/>.</param>
+        /// <returns>An <see cref="IModelBinder"/>.</returns>
+        IModelBinder GetBinder(ModelBinderProviderContext context);
+    }
+}

src/Microsoft.AspNetCore.Mvc.Abstractions/ModelBinding/Metadata/ModelMetadataIdentity.cs

@@ -3,13 +3,14 @@
 
 using System;
 using Microsoft.AspNetCore.Mvc.Abstractions;
+using Microsoft.Extensions.Internal;
 
 namespace Microsoft.AspNetCore.Mvc.ModelBinding.Metadata
 {
     /// <summary>
     /// A key type which identifies a <see cref="ModelMetadata"/>.
     /// </summary>
-    public struct ModelMetadataIdentity
+    public struct ModelMetadataIdentity : IEquatable<ModelMetadataIdentity>
     {
         /// <summary>
         /// Creates a <see cref="ModelMetadataIdentity"/> for the provided model <see cref="Type"/>.
@@ -98,5 +99,31 @@ public ModelMetadataKind MetadataKind
         /// the current instance represents a type.
         /// </summary>
         public string Name { get; private set; }
+
+        /// <inheritdoc />
+        public bool Equals(ModelMetadataIdentity other)
+        {
+            return
+                ContainerType == other.ContainerType &&
+                ModelType == other.ModelType &&
+                Name == other.Name;
+        }
+
+        /// <inheritdoc />
+        public override bool Equals(object obj)
+        {
+            var other = obj as ModelMetadataIdentity?;
+            return other.HasValue && Equals(other.Value);
+        }
+
+        /// <inheritdoc />
+        public override int GetHashCode()
+        {
+            var hash = new HashCodeCombiner();
+            hash.Add(ContainerType);
+            hash.Add(ModelType);
+            hash.Add(Name, StringComparer.Ordinal);
+            return hash;
+        }
     }
 }

src/Microsoft.AspNetCore.Mvc.Abstractions/ModelBinding/ModelBinderProviderContext.cs

@@ -0,0 +1,33 @@
+// 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.
+
+namespace Microsoft.AspNetCore.Mvc.ModelBinding
+{
+    /// <summary>
+    /// A context object for <see cref="IModelBinderProvider.GetBinder"/>.
+    /// </summary>
+    public abstract class ModelBinderProviderContext
+    {
+        /// <summary>
+        /// Creates an <see cref="IModelBinder"/> for the given <paramref name="metadata"/>.
+        /// </summary>
+        /// <param name="metadata">The <see cref="ModelMetadata"/> for the model.</param>
+        /// <returns>An <see cref="IModelBinder"/>.</returns>
+        public abstract IModelBinder CreateBinder(ModelMetadata metadata);
+
+        /// <summary>
+        /// Gets the <see cref="BindingInfo"/>. May be <c>null</c>.
+        /// </summary>
+        public abstract BindingInfo BindingInfo { get; }
+
+        /// <summary>
+        /// Gets the <see cref="ModelMetadata"/>.
+        /// </summary>
+        public abstract ModelMetadata Metadata { get; }
+
+        /// <summary>
+        /// Gets the <see cref="IModelMetadataProvider"/>.
+        /// </summary>
+        public abstract IModelMetadataProvider MetadataProvider { get; }
+    }
+}

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

@@ -16,28 +16,12 @@ public abstract class ModelBindingContext
         /// </summary>
         public abstract string BinderModelName { get; set; }
 
-        /// <summary>
-        /// Gets the <see cref="Type"/> of an <see cref="IModelBinder"/> associated with the
-        /// <see cref="Model"/>.
-        /// </summary>
-        public abstract Type BinderType { get; set; }
-
         /// <summary>
         /// Gets or sets a value which represents the <see cref="ModelBinding.BindingSource"/> associated with the
         /// <see cref="Model"/>.
         /// </summary>
         public abstract BindingSource BindingSource { get; set; }
 
-        /// <summary>
-        /// 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 abstract bool FallbackToEmptyPrefix { get; set; }
-
         /// <summary>
         /// Gets or sets the name of the current field being bound.
         /// </summary>

src/Microsoft.AspNetCore.Mvc.Abstractions/ModelBinding/ModelMetadata.cs

@@ -16,7 +16,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
     /// A metadata representation of a model type, property or parameter.
     /// </summary>
     [DebuggerDisplay("{DebuggerToString(),nq}")]
-    public abstract class ModelMetadata
+    public abstract class ModelMetadata : IEquatable<ModelMetadata>
     {
         /// <summary>
         /// The default value of <see cref="ModelMetadata.Order"/>.
@@ -378,6 +378,36 @@ public string GetDisplayName()
             return DisplayName ?? PropertyName ?? ModelType.Name;
         }
 
+        /// <inheritdoc />
+        public bool Equals(ModelMetadata other)
+        {
+            if (object.ReferenceEquals(this, other))
+            {
+                return true;
+            }
+
+            if (other == null)
+            {
+                return false;
+            }
+            else
+            {
+                return Identity.Equals(other.Identity);
+            }
+        }
+
+        /// <inheritdoc />
+        public override bool Equals(object obj)
+        {
+            return base.Equals(obj as ModelMetadata);
+        }
+
+        /// <inheritdoc />
+        public override int GetHashCode()
+        {
+            return Identity.GetHashCode();
+        }
+
         private void InitializeTypeInformation()
         {
             Debug.Assert(ModelType != null);

src/Microsoft.AspNetCore.Mvc.Abstractions/ModelBinding/OperationBindingContext.cs

@@ -35,11 +35,6 @@ public class OperationBindingContext
         /// </summary>
         public IValueProvider ValueProvider { get; set; }
 
-        /// <summary>
-        /// Gets or sets the <see cref="IModelBinder"/> associated with this context.
-        /// </summary>
-        public IModelBinder ModelBinder { get; set; }
-
         /// <summary>
         /// Gets or sets the <see cref="IModelMetadataProvider"/> associated with this context.
         /// </summary>

src/Microsoft.AspNetCore.Mvc.Core/ControllerBase.cs

@@ -27,6 +27,7 @@ public abstract class ControllerBase
     {
         private ControllerContext _controllerContext;
         private IModelMetadataProvider _metadataProvider;
+        private IModelBinderFactory _modelBinderFactory;
         private IObjectModelValidator _objectValidator;
         private IUrlHelper _url;
 
@@ -141,6 +142,31 @@ public IModelMetadataProvider MetadataProvider
             }
         }
 
+        /// <summary>
+        /// Gets or sets the <see cref="IModelBinderFactory"/>.
+        /// </summary>
+        public IModelBinderFactory ModelBinderFactory
+        {
+            get
+            {
+                if (_modelBinderFactory == null)
+                {
+                    _modelBinderFactory = HttpContext?.RequestServices?.GetRequiredService<IModelBinderFactory>();
+                }
+
+                return _modelBinderFactory;
+            }
+            set
+            {
+                if (value == null)
+                {
+                    throw new ArgumentNullException(nameof(value));
+                }
+
+                _modelBinderFactory = value;
+            }
+        }
+
         /// <summary>
         /// Gets or sets the <see cref="IUrlHelper"/>.
         /// </summary>
@@ -1139,7 +1165,7 @@ public virtual Task<bool> TryUpdateModelAsync<TModel>(
                 prefix,
                 ControllerContext,
                 MetadataProvider,
-                new CompositeModelBinder(ControllerContext.ModelBinders),
+                ModelBinderFactory,
                 valueProvider,
                 ControllerContext.InputFormatters,
                 ObjectValidator,
@@ -1179,7 +1205,7 @@ public Task<bool> TryUpdateModelAsync<TModel>(
                 prefix,
                 ControllerContext,
                 MetadataProvider,
-                new CompositeModelBinder(ControllerContext.ModelBinders),
+                ModelBinderFactory,
                 new CompositeValueProvider(ControllerContext.ValueProviders),
                 ControllerContext.InputFormatters,
                 ObjectValidator,
@@ -1219,7 +1245,7 @@ public Task<bool> TryUpdateModelAsync<TModel>(
                 prefix,
                 ControllerContext,
                 MetadataProvider,
-                new CompositeModelBinder(ControllerContext.ModelBinders),
+                ModelBinderFactory,
                 new CompositeValueProvider(ControllerContext.ValueProviders),
                 ControllerContext.InputFormatters,
                 ObjectValidator,
@@ -1267,7 +1293,7 @@ public Task<bool> TryUpdateModelAsync<TModel>(
                 prefix,
                 ControllerContext,
                 MetadataProvider,
-                new CompositeModelBinder(ControllerContext.ModelBinders),
+                ModelBinderFactory,
                 valueProvider,
                 ControllerContext.InputFormatters,
                 ObjectValidator,
@@ -1314,7 +1340,7 @@ public Task<bool> TryUpdateModelAsync<TModel>(
                 prefix,
                 ControllerContext,
                 MetadataProvider,
-                new CompositeModelBinder(ControllerContext.ModelBinders),
+                ModelBinderFactory,
                 valueProvider,
                 ControllerContext.InputFormatters,
                 ObjectValidator,
@@ -1353,7 +1379,7 @@ public virtual Task<bool> TryUpdateModelAsync(
                 prefix,
                 ControllerContext,
                 MetadataProvider,
-                new CompositeModelBinder(ControllerContext.ModelBinders),
+                ModelBinderFactory,
                 new CompositeValueProvider(ControllerContext.ValueProviders),
                 ControllerContext.InputFormatters,
                 ObjectValidator,
@@ -1405,7 +1431,7 @@ public Task<bool> TryUpdateModelAsync(
                 prefix,
                 ControllerContext,
                 MetadataProvider,
-                new CompositeModelBinder(ControllerContext.ModelBinders),
+                ModelBinderFactory,
                 valueProvider,
                 ControllerContext.InputFormatters,
                 ObjectValidator,

src/Microsoft.AspNetCore.Mvc.Core/ControllerContext.cs

@@ -17,7 +17,6 @@ namespace Microsoft.AspNetCore.Mvc
     public class ControllerContext : ActionContext
     {
         private FormatterCollection<IInputFormatter> _inputFormatters;
-        private IList<IModelBinder> _modelBinders;
         private IList<IModelValidatorProvider> _validatorProviders;
         private IList<IValueProvider> _valueProviders;
 
@@ -81,31 +80,6 @@ public virtual FormatterCollection<IInputFormatter> InputFormatters
             }
         }
 
-        /// <summary>
-        /// Gets or sets the list of <see cref="IModelBinder"/> instances for the current request.
-        /// </summary>
-        public virtual IList<IModelBinder> ModelBinders
-        {
-            get
-            {
-                if (_modelBinders == null)
-                {
-                    _modelBinders = new List<IModelBinder>();
-                }
-
-                return _modelBinders;
-            }
-            set
-            {
-                if (value == null)
-                {
-                    throw new ArgumentNullException(nameof(value));
-                }
-
-                _modelBinders = value;
-            }
-        }
-
         /// <summary>
         /// Gets or sets the list of <see cref="IModelValidatorProvider"/> instances for the current request.
         /// </summary>

src/Microsoft.AspNetCore.Mvc.Core/DependencyInjection/MvcCoreServiceCollectionExtensions.cs

@@ -143,6 +143,7 @@ internal static void AddMvcCoreServices(IServiceCollection services)
                 var options = serviceProvider.GetRequiredService<IOptions<MvcOptions>>().Value;
                 return new DefaultCompositeMetadataDetailsProvider(options.ModelMetadataDetailsProviders);
             }));
+            services.TryAddSingleton<IModelBinderFactory, ModelBinderFactory>();
             services.TryAddSingleton<IObjectModelValidator, DefaultObjectValidator>();
             services.TryAddSingleton<ValidatorCache>();
             services.TryAddSingleton<ClientValidatorCache>();

src/Microsoft.AspNetCore.Mvc.Core/Internal/ControllerActionInvoker.cs

@@ -32,7 +32,6 @@ public ControllerActionInvoker(
             ControllerActionDescriptor descriptor,
             IReadOnlyList<IInputFormatter> inputFormatters,
             IControllerActionArgumentBinder argumentBinder,
-            IReadOnlyList<IModelBinder> modelBinders,
             IReadOnlyList<IModelValidatorProvider> modelValidatorProviders,
             IReadOnlyList<IValueProviderFactory> valueProviderFactories,
             ILogger logger,
@@ -42,7 +41,6 @@ public ControllerActionInvoker(
                   actionContext,
                   controllerActionInvokerCache,
                   inputFormatters,
-                  modelBinders,
                   modelValidatorProviders,
                   valueProviderFactories,
                   logger,

src/Microsoft.AspNetCore.Mvc.Core/Internal/ControllerActionInvokerProvider.cs

@@ -21,7 +21,6 @@ public class ControllerActionInvokerProvider : IActionInvokerProvider
         private readonly IControllerFactory _controllerFactory;
         private readonly ControllerActionInvokerCache _controllerActionInvokerCache;
         private readonly IReadOnlyList<IInputFormatter> _inputFormatters;
-        private readonly IReadOnlyList<IModelBinder> _modelBinders;
         private readonly IReadOnlyList<IModelValidatorProvider> _modelValidatorProviders;
         private readonly IReadOnlyList<IValueProviderFactory> _valueProviderFactories;
         private readonly int _maxModelValidationErrors;
@@ -40,7 +39,6 @@ public ControllerActionInvokerProvider(
             _controllerActionInvokerCache = controllerActionInvokerCache;
             _argumentBinder = argumentBinder;
             _inputFormatters = optionsAccessor.Value.InputFormatters.ToArray();
-            _modelBinders = optionsAccessor.Value.ModelBinders.ToArray();
             _modelValidatorProviders = optionsAccessor.Value.ModelValidatorProviders.ToArray();
             _valueProviderFactories = optionsAccessor.Value.ValueProviderFactories.ToArray();
             _maxModelValidationErrors = optionsAccessor.Value.MaxModelValidationErrors;
@@ -72,7 +70,6 @@ public void OnProvidersExecuting(ActionInvokerProviderContext context)
                     actionDescriptor,
                     _inputFormatters,
                     _argumentBinder,
-                    _modelBinders,
                     _modelValidatorProviders,
                     _valueProviderFactories,
                     _logger,