Set model prefix for [ApiController]

Infers the 'empty' model prefix for complex types that are read from the value
providers. This gives us better defaults when using the parameter object
pattern with respect to swagger/API explorer.

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

@@ -64,6 +64,11 @@ namespace Microsoft.AspNetCore.Mvc.Internal
                     controllerModel.ApiExplorer.IsVisible = true;
                 }
 
+                if (isApiController)
+                {
+                    InferBoundPropertyModelPrefixes(controllerModel);
+                }
+
                 var controllerHasSelectorModel = controllerModel.Selectors.Any(s => s.AttributeRouteModel != null);
 
                 foreach (var actionModel in controllerModel.Actions)
@@ -79,6 +84,8 @@ namespace Microsoft.AspNetCore.Mvc.Internal
 
                     InferParameterBindingSources(actionModel);
 
+                    InferParameterModelPrefixes(actionModel);
+
                     AddMultipartFormDataConsumesAttribute(actionModel);
                 }
             }
@@ -179,6 +186,50 @@ namespace Microsoft.AspNetCore.Mvc.Internal
             }
         }
 
+        // For any complex types that are bound from value providers, set the prefix
+        // to the empty prefix by default. This makes binding much more predictable
+        // and describable via ApiExplorer
+
+        // internal for testing
+        internal void InferBoundPropertyModelPrefixes(ControllerModel controllerModel)
+        {
+            foreach (var property in controllerModel.ControllerProperties)
+            {
+                if (property.BindingInfo != null &&
+                    property.BindingInfo.BinderModelName == null &&
+                    property.BindingInfo.BindingSource != null &&
+                    !property.BindingInfo.BindingSource.IsGreedy)
+                {
+                    var metadata = _modelMetadataProvider.GetMetadataForProperty(
+                        controllerModel.ControllerType,
+                        property.PropertyInfo.Name);
+                    if (metadata.IsComplexType)
+                    {
+                        property.BindingInfo.BinderModelName = string.Empty;
+                    }
+                }
+            }
+        }
+        
+        // internal for testing
+        internal void InferParameterModelPrefixes(ActionModel actionModel)
+        {
+            foreach (var parameter in actionModel.Parameters)
+            {
+                if (parameter.BindingInfo != null &&
+                    parameter.BindingInfo.BinderModelName == null &&
+                    parameter.BindingInfo.BindingSource != null &&
+                    !parameter.BindingInfo.BindingSource.IsGreedy)
+                {
+                    var metadata = GetParameterMetadata(parameter);
+                    if (metadata.IsComplexType)
+                    {
+                        parameter.BindingInfo.BinderModelName = string.Empty;
+                    }
+                }
+            }
+        }
+
         // Internal for unit testing.
         internal BindingSource InferBindingSourceForParameter(ParameterModel parameter)
         {
@@ -189,16 +240,7 @@ namespace Microsoft.AspNetCore.Mvc.Internal
             }
             else
             {
-                ModelMetadata parameterMetadata;
-                if (_modelMetadataProvider is ModelMetadataProvider modelMetadataProvider)
-                {
-                    parameterMetadata = modelMetadataProvider.GetMetadataForParameter(parameter.ParameterInfo);
-                }
-                else
-                {
-                    parameterMetadata = _modelMetadataProvider.GetMetadataForType(parameter.ParameterInfo.ParameterType);
-                }
-
+                var parameterMetadata = GetParameterMetadata(parameter);
                 if (parameterMetadata != null)
                 {
                     var bindingSource = parameterMetadata.IsComplexType ?
@@ -234,5 +276,17 @@ namespace Microsoft.AspNetCore.Mvc.Internal
 
             return parameterExistsInSomeRoute;
         }
+
+        private ModelMetadata GetParameterMetadata(ParameterModel parameter)
+        {
+            if (_modelMetadataProvider is ModelMetadataProvider modelMetadataProvider)
+            {
+                return modelMetadataProvider.GetMetadataForParameter(parameter.ParameterInfo);
+            }
+            else
+            {
+                return _modelMetadataProvider.GetMetadataForType(parameter.ParameterInfo.ParameterType);
+            }
+        }
     }
 }

test/Microsoft.AspNetCore.Mvc.Core.Test/Internal/ApiBehaviorApplicationModelProviderTest.cs

@@ -398,6 +398,38 @@ namespace Microsoft.AspNetCore.Mvc.Internal
             Assert.Same(BindingSource.Query, result);
         }
 
+        [Fact]
+        public void InferBoundPropertyModelPrefixes_SetsModelPrefix_ForComplexTypeFromValueProvider()
+        {
+            // Arrange
+            var controller = GetControllerModel(typeof(ControllerWithBoundProperty));
+
+            var provider = GetProvider();
+
+            // Act
+            provider.InferBoundPropertyModelPrefixes(controller);
+
+            // Assert
+            var property = Assert.Single(controller.ControllerProperties);
+            Assert.Equal(string.Empty, property.BindingInfo.BinderModelName);
+        }
+
+        [Fact]
+        public void InferParameterModelPrefixes_SetsModelPrefix_ForComplexTypeFromValueProvider()
+        {
+            // Arrange
+            var action = GetActionModel(typeof(ControllerWithBoundProperty), nameof(ControllerWithBoundProperty.SomeAction));
+
+            var provider = GetProvider();
+
+            // Act
+            provider.InferParameterModelPrefixes(action);
+
+            // Assert
+            var parameter = Assert.Single(action.Parameters);
+            Assert.Equal(string.Empty, parameter.BindingInfo.BinderModelName);
+        }
+
         [Fact]
         public void AddMultipartFormDataConsumesAttribute_NoOpsIfBehaviorIsDisabled()
         {
@@ -483,6 +515,12 @@ namespace Microsoft.AspNetCore.Mvc.Internal
             return context;
         }
 
+        private static ControllerModel GetControllerModel(Type controllerType)
+        {
+            var context = GetContext(controllerType);
+            return Assert.Single(context.Result.Controllers);
+        }
+
         private static ActionModel GetActionModel(Type controllerType, string actionName)
         {
             var context = GetContext(controllerType);
@@ -622,5 +660,14 @@ namespace Microsoft.AspNetCore.Mvc.Internal
             public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
                 => sourceType == typeof(string);
         }
+
+        [ApiController]
+        private class ControllerWithBoundProperty
+        {
+            [FromQuery]
+            public TestModel TestProperty { get; set; }
+
+            public IActionResult SomeAction([FromQuery] TestModel test) => null;
+        }
     }
 }

test/Microsoft.AspNetCore.Mvc.FunctionalTests/ApiBehaviorTest.cs

@@ -124,5 +124,47 @@ namespace Microsoft.AspNetCore.Mvc.FunctionalTests
             Assert.Equal(name, result.Name);
             Assert.Equal(email, result.Email);
         }
+
+        [Fact]
+        public async Task ActionsWithApiBehavior_InferEmptyPrefixForComplexValueProviderModel_Success()
+        {
+            // Arrange
+            var id = 31;
+            var name = "test_user";
+            var email = "email@test.com";
+            var url = $"/contact/ActionWithInferredEmptyPrefix?name={name}&contactid={id}&email={email}";
+
+            // Act
+            var response = await Client.GetAsync(url);
+
+            // Assert
+            Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+
+            var result = await response.Content.ReadAsAsync<Contact>();
+            Assert.Equal(id, result.ContactId);
+            Assert.Equal(name, result.Name);
+            Assert.Equal(email, result.Email);
+        }
+
+        [Fact]
+        public async Task ActionsWithApiBehavior_InferEmptyPrefixForComplexValueProviderModel_Ignored()
+        {
+            // Arrange
+            var id = 31;
+            var name = "test_user";
+            var email = "email@test.com";
+            var url = $"/contact/ActionWithInferredEmptyPrefix?contact.name={name}&contact.contactid={id}&contact.email={email}";
+
+            // Act
+            var response = await Client.GetAsync(url);
+
+            // Assert
+            Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+
+            var result = await response.Content.ReadAsAsync<Contact>();
+            Assert.Equal(0, result.ContactId);
+            Assert.Null(result.Name);
+            Assert.Null(result.Email);
+        }
     }
 }

test/WebSites/BasicWebSite/Controllers/ContactApiController.cs

@@ -61,5 +61,11 @@ namespace BasicWebSite
                 Email = email,
             };
         }
+
+        [HttpGet("[action]")]
+        public ActionResult<Contact> ActionWithInferredEmptyPrefix([FromQuery] Contact contact)
+        {
+            return contact;
+        }
     }
 }