Fix for #1837 - Determine model type at runtime for TryUpdateModel and added a test

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

@@ -138,7 +138,8 @@ namespace Microsoft.AspNet.Mvc
         {
             var modelMetadata = metadataProvider.GetMetadataForType(
                 modelAccessor: null,
-                modelType: typeof(TModel));
+                modelType: model.GetType());
+
             var operationBindingContext = new OperationBindingContext
             {
                 ModelBinder = modelBinder,

test/Microsoft.AspNet.Mvc.FunctionalTests/ModelBindingTests.cs

@@ -1429,5 +1429,26 @@ namespace Microsoft.AspNet.Mvc.FunctionalTests
             Assert.Equal("test.txt", fileDetails.Filename);
             Assert.Equal("Test Content", fileDetails.Content);
         }
+
+        [Fact]
+        public async Task TryUpdateModel_ReturnDerivedAndBaseProperties()
+        {
+            // Arrange
+            var server = TestServer.Create(_services, _app);
+            var client = server.CreateClient();
+
+            // Act
+            var response = await client.GetStringAsync("http://localhost/TryUpdateModel/" +
+                "GetEmployeeAsync_BindToBaseDeclaredType" +
+                "?Parent.Name=fatherName&Parent.Parent.Name=grandFatherName&Department=Sales");
+
+            // Assert
+            var employee = JsonConvert.DeserializeObject<Employee>(response);
+            Assert.Equal("fatherName", employee.Parent.Name);
+            Assert.Equal("Sales", employee.Department);
+
+            // Round-tripped value includes descendent instances for all properties with data in the request.
+            Assert.Equal("grandFatherName", employee.Parent.Parent.Name);
+        }
     }
 }

test/WebSites/ModelBindingWebSite/Controllers/TryUpdateModelController.cs

@@ -98,6 +98,16 @@ namespace ModelBindingWebSite.Controllers
             return user;
         }
 
+        public async Task<Employee> GetEmployeeAsync_BindToBaseDeclaredType()
+        {
+            var employee = new Employee();
+            await TryUpdateModelAsync<Person>(
+                employee,
+                prefix: string.Empty);
+
+            return employee;
+        }
+
         private User GetUser(int id)
         {
             return new User