[Fixes #5686] Extend `ModelMetadata` to reduce ugliness

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

@@ -17,7 +17,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
     /// A metadata representation of a model type, property or parameter.
     /// </summary>
     [DebuggerDisplay("{DebuggerToString(),nq}")]
-    public abstract class ModelMetadata : IEquatable<ModelMetadata>
+    public abstract class ModelMetadata : IEquatable<ModelMetadata>, IModelMetadataProvider
     {
         /// <summary>
         /// The default value of <see cref="ModelMetadata.Order"/>.
@@ -42,6 +42,17 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         /// </summary>
         public Type ContainerType { get { return Identity.ContainerType; } }
 
+        /// <summary>
+        /// Gets the metadata of the container type that the current instance is part of.
+        /// </summary>
+        public virtual ModelMetadata ContainerMetadata
+        {
+            get
+            {
+                throw new NotImplementedException();
+            }
+        }
+        
         /// <summary>
         /// Gets a value indicating the kind of metadata element represented by the current instance.
         /// </summary>
@@ -474,5 +485,17 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
                 return $"ModelMetadata (Property: '{ContainerType.Name}.{PropertyName}' Type: '{ModelType.Name}')";
             }
         }
+
+        /// <inheritdoc />
+        public virtual ModelMetadata GetMetadataForType(Type modelType)
+        {
+            throw new NotImplementedException();
+        }
+
+        /// <inheritdoc />
+        public virtual IEnumerable<ModelMetadata> GetMetadataForProperties(Type modelType)
+        {
+            throw new NotImplementedException();
+        }
     }
 }

src/Microsoft.AspNetCore.Mvc.Core/ModelBinding/Metadata/DefaultMetadataDetails.cs

@@ -68,5 +68,10 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Metadata
         /// Gets or sets the <see cref="Metadata.ValidationMetadata"/>
         /// </summary>
         public ValidationMetadata ValidationMetadata { get; set; }
+
+        /// <summary>
+        /// Gets or sets the <see cref="ModelMetadata"/> of the container type.
+        /// </summary>
+        public ModelMetadata ContainerMetadata { get; set; }
     }
 }

src/Microsoft.AspNetCore.Mvc.Core/ModelBinding/Metadata/DefaultModelMetadata.cs

@@ -96,6 +96,15 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Metadata
             }
         }
 
+        /// <inheritdoc />
+        public override ModelMetadata ContainerMetadata
+        {
+            get
+            {
+                return _details.ContainerMetadata;
+            }
+        }
+
         /// <summary>
         /// Gets the <see cref="Metadata.BindingMetadata"/> for the current instance.
         /// </summary>
@@ -597,5 +606,17 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Metadata
                 return _details.PropertySetter;
             }
         }
+
+        /// <inheritdoc />
+        public override ModelMetadata GetMetadataForType(Type modelType)
+        {
+            return _provider.GetMetadataForType(modelType);
+        }
+
+        /// <inheritdoc />
+        public override IEnumerable<ModelMetadata> GetMetadataForProperties(Type modelType)
+        {
+            return _provider.GetMetadataForProperties(modelType);
+        }
     }
 }

src/Microsoft.AspNetCore.Mvc.Core/ModelBinding/Metadata/DefaultModelMetadataProvider.cs

@@ -87,6 +87,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Metadata
                 var properties = new ModelMetadata[propertyDetails.Length];
                 for (var i = 0; i < properties.Length; i++)
                 {
+                    propertyDetails[i].ContainerMetadata = cacheEntry.Metadata;
                     properties[i] = CreateModelMetadata(propertyDetails[i]);
                 }
 

test/Microsoft.AspNetCore.Mvc.Abstractions.Test/ModelBinding/ModelMetadataTest.cs

@@ -302,6 +302,36 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
             Assert.Equal("String", result);
         }
 
+        [Fact]
+        public void GetContainerMetadata_ThrowsNotImplementedException_ByDefault()
+        {
+            // Arrange
+            var metadata = new TestModelMetadata(typeof(DerivedList));
+
+            // Act & Assert
+            Assert.Throws<NotImplementedException>(() => metadata.ContainerMetadata);
+        }
+
+        [Fact]
+        public void GetMetadataForType_ByDefaultThrows_NotImplementedException()
+        {
+            // Arrange
+            var metadata = new TestModelMetadata(typeof(string));
+
+            // Act & Assert
+            var result = Assert.Throws<NotImplementedException>(() => metadata.GetMetadataForType(typeof(string)));
+        }
+
+        [Fact]
+        public void GetMetadataForProperties_ByDefaultThrows_NotImplementedException()
+        {
+            // Arrange
+            var metadata = new TestModelMetadata(typeof(string));
+
+            // Act & Assert
+            var result = Assert.Throws<NotImplementedException>(() => metadata.GetMetadataForProperties(typeof(string)));
+        }
+
         private class TestModelMetadata : ModelMetadata
         {
             private string _displayName;

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

@@ -57,6 +57,33 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Metadata
             Assert.Same(metadata1, metadata2);
         }
 
+        [Fact]
+        public void GetMetadataForProperties_IncludesContainerMetadataForAllProperties()
+        {
+            // Arrange
+            var provider = CreateProvider();
+            var modelType = typeof(ModelType);
+
+            // Act
+            var metadata = provider.GetMetadataForProperties(modelType).ToArray();
+
+            // Assert
+            Assert.Collection(
+                metadata,
+                (propertyMetadata) =>
+                {
+                    Assert.Equal("Property1", propertyMetadata.PropertyName);
+                    Assert.NotNull(propertyMetadata.ContainerMetadata);
+                    Assert.Equal(modelType, propertyMetadata.ContainerMetadata.ModelType);
+                },
+                (propertyMetadata) =>
+                {
+                    Assert.Equal("Property2", propertyMetadata.PropertyName);
+                    Assert.NotNull(propertyMetadata.ContainerMetadata);
+                    Assert.Equal(modelType, propertyMetadata.ContainerMetadata.ModelType);
+                });
+        }
+
         [Fact]
         public void GetMetadataForProperties_IncludesAllProperties()
         {

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

@@ -744,6 +744,46 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Metadata
             Assert.False(validateChildren);
         }
 
+        [Fact]
+        public void GetMetadataForType_CallsProvider()
+        {
+            // Arrange
+            var detailsProvider = new Mock<ICompositeMetadataDetailsProvider>();
+            var key = ModelMetadataIdentity.ForType(typeof(string));
+            var cache = new DefaultMetadataDetails(key, new ModelAttributes(new object[0]));
+            var metadataProvider = new Mock<IModelMetadataProvider>();
+            metadataProvider
+                .Setup(mp => mp.GetMetadataForType(typeof(string)))
+                .Verifiable();
+            var metadata1 = new DefaultModelMetadata(metadataProvider.Object, detailsProvider.Object, cache);
+
+            // Act
+            var metadata2 = metadata1.GetMetadataForType(typeof(string));
+
+            // Assert
+            metadataProvider.VerifyAll();
+        }
+
+        [Fact]
+        public void GetMetadataForProperties_CallsProvider()
+        {
+            // Arrange
+            var detailsProvider = new Mock<ICompositeMetadataDetailsProvider>();
+            var key = ModelMetadataIdentity.ForType(typeof(string));
+            var cache = new DefaultMetadataDetails(key, new ModelAttributes(new object[0]));
+            var metadataProvider = new Mock<IModelMetadataProvider>();
+            metadataProvider
+                .Setup(mp => mp.GetMetadataForProperties(typeof(Exception)))
+                .Verifiable();
+            var metadata1 = new DefaultModelMetadata(metadataProvider.Object, detailsProvider.Object, cache);
+
+            // Act
+            var metadata2 = metadata1.GetMetadataForProperties(typeof(Exception));
+
+            // Assert
+            metadataProvider.VerifyAll();
+        }
+
         private void ActionMethod(string input)
         {
         }