Fix Create Property Model Name for Complex Objects

src/Mvc/Mvc.Core/src/ModelBinding/Binders/ComplexObjectModelBinder.cs

@@ -364,7 +364,7 @@ internal void CreateModel(ModelBindingContext bindingContext)
             }
 
             var fieldName = property.BinderModelName ?? property.PropertyName!;
-            var modelName = ModelNames.CreatePropertyModelName(bindingContext.ModelName, fieldName);
+            var modelName = ModelNames.CreatePropertyModelNameOptimized(bindingContext.ModelName, fieldName);
             var result = await BindPropertyAsync(bindingContext, property, propertyBinder, fieldName, modelName);
 
             if (result.IsModelSet)

src/Mvc/Mvc.Core/src/ModelBinding/ModelNames.cs

@@ -61,4 +61,44 @@ public static string CreatePropertyModelName(string? prefix, string? propertyNam
 
         return prefix + "." + propertyName;
     }
+
+    /// <summary>
+    /// Create a model property name using a prefix and a property name,
+    /// with a small optimization to avoid redundancy.
+    ///
+    /// For example, if both <paramref name="prefix"/> and <paramref name="propertyName"/> are "parameter"
+    /// (ignoring case), the result will be just "parameter" instead of "parameter.Parameter".
+    /// </summary>
+    /// <param name="prefix">The prefix to use.</param>
+    /// <param name="propertyName">The property name.</param>
+    /// <returns>The property model name.</returns>
+    public static string CreatePropertyModelNameOptimized(string? prefix, string? propertyName)
+    {
+        if (string.IsNullOrEmpty(prefix))
+        {
+            return propertyName ?? string.Empty;
+        }
+
+        if (string.IsNullOrEmpty(propertyName))
+        {
+            return prefix ?? string.Empty;
+        }
+
+        if (propertyName.StartsWith('['))
+        {
+            // The propertyName might represent an indexer access, in which case combining
+            // with a 'dot' would be invalid. This case occurs only when called from ValidationVisitor.
+            return prefix + propertyName;
+        }
+
+        if (string.Equals(prefix, propertyName, StringComparison.OrdinalIgnoreCase))
+        {
+            // if we are dealing with with something like:
+            // prefix = parameter and propertyName = parameter
+            // it should fallback to the property name.
+            return propertyName;
+        }
+
+        return prefix + "." + propertyName;
+    }
 }

src/Mvc/Mvc.Core/src/PublicAPI.Unshipped.txt

@@ -6,3 +6,4 @@ Microsoft.AspNetCore.Mvc.ProducesDefaultResponseTypeAttribute.Description.get ->
 Microsoft.AspNetCore.Mvc.ProducesDefaultResponseTypeAttribute.Description.set -> void
 Microsoft.AspNetCore.Mvc.ProducesResponseTypeAttribute.Description.get -> string?
 Microsoft.AspNetCore.Mvc.ProducesResponseTypeAttribute.Description.set -> void
+static Microsoft.AspNetCore.Mvc.ModelBinding.ModelNames.CreatePropertyModelNameOptimized(string? prefix, string? propertyName) -> string!

src/Mvc/test/Mvc.IntegrationTests/CollectionModelBinderIntegrationTest.cs

@@ -338,6 +338,74 @@ public async Task CollectionModelBinder_BindsListOfComplexType_WithRequiredPrope
         Assert.Equal("A value for the 'Name' parameter or property was not provided.", error.ErrorMessage);
     }
 
+    class TestClass
+    {
+        public TestClass2 Parameter { get; set; }
+    }
+
+    class TestClass2
+    {
+        public string Parameter { get; set; } = "";
+    }
+
+    [Fact(Skip = "Nested properties are more complex to deal with it. See https://github.com/dotnet/aspnetcore/pull/62459 for more info.")]
+    public async Task CollectionModelBinder_CanBind_NestedProperties_WithSameNameOfParameter()
+    {
+        // Arrange
+        var parameterBinder = ModelBindingTestHelper.GetParameterBinder();
+        var parameter = new ParameterDescriptor()
+        {
+            Name = "parameter",
+            ParameterType = typeof(TestClass)
+        };
+
+        var testContext = ModelBindingTestHelper.GetTestContext(request =>
+        {
+            request.QueryString = new QueryString("?parameter.parameter=testing");
+        });
+
+        var modelState = testContext.ModelState;
+
+        // Act
+        var modelBindingResult = await parameterBinder.BindModelAsync(parameter, testContext);
+
+        // Assert
+        Assert.True(modelBindingResult.IsModelSet);
+
+        var model = Assert.IsType<TestClass>(modelBindingResult.Model);
+        Assert.Equal("testing", model.Parameter.Parameter);
+        Assert.True(modelState.IsValid);
+    }
+
+    [Fact]
+    public async Task CollectionModelBinder_CanBind_SimpleProperties_WithSameNameOfParameter()
+    {
+        // Arrange
+        var parameterBinder = ModelBindingTestHelper.GetParameterBinder();
+        var parameter = new ParameterDescriptor()
+        {
+            Name = "parameter",
+            ParameterType = typeof(TestClass2)
+        };
+
+        var testContext = ModelBindingTestHelper.GetTestContext(request =>
+        {
+            request.QueryString = new QueryString("?parameter=testing");
+        });
+
+        var modelState = testContext.ModelState;
+
+        // Act
+        var modelBindingResult = await parameterBinder.BindModelAsync(parameter, testContext);
+
+        // Assert
+        Assert.True(modelBindingResult.IsModelSet);
+
+        var model = Assert.IsType<TestClass2>(modelBindingResult.Model);
+        Assert.Equal("testing", model.Parameter);
+        Assert.True(modelState.IsValid);
+    }
+
     [Fact]
     public async Task CollectionModelBinder_BindsListOfComplexType_WithRequiredProperty_WithExplicitPrefix_PartialData()
     {