Added consistent model property to view result variants (#4901)

* Added consistent model property/tests to ViewResult, PartialViewResult, ViewComponentResult. This resolves #4813.

* Removed unnecessary model asserts

* Removed redundant model checking

src/Microsoft.AspNetCore.Mvc.ViewFeatures/PartialViewResult.cs

@@ -29,6 +29,11 @@ namespace Microsoft.AspNetCore.Mvc
         /// </remarks>
         public string ViewName { get; set; }
 
+        /// <summary>
+        /// Gets the view data model.
+        /// </summary>
+        public object Model => ViewData?.Model;
+
         /// <summary>
         /// Gets or sets the <see cref="ViewDataDictionary"/> used for rendering the view for this result.
         /// </summary>

src/Microsoft.AspNetCore.Mvc.ViewFeatures/ViewComponentResult.cs

@@ -20,21 +20,11 @@ namespace Microsoft.AspNetCore.Mvc
         /// </summary>
         public object Arguments { get; set; }
 
-        /// <summary>
-        /// Gets or sets the Content-Type header for the response.
-        /// </summary>
-        public string ContentType { get; set; }
-
         /// <summary>
         /// Gets or sets the HTTP status code.
         /// </summary>
         public int? StatusCode { get; set; }
 
-        /// <summary>
-        /// Gets or sets the <see cref="ITempDataDictionary"/> for this result.
-        /// </summary>
-        public ITempDataDictionary TempData { get; set; }
-
         /// <summary>
         /// Gets or sets the name of the view component to invoke. Will be ignored if <see cref="ViewComponentType"/>
         /// is set to a non-<c>null</c> value.
@@ -46,11 +36,21 @@ namespace Microsoft.AspNetCore.Mvc
         /// </summary>
         public Type ViewComponentType { get; set; }
 
+        /// <summary>
+        /// Get the view data model.
+        /// </summary>
+        public object Model => ViewData?.Model;
+
         /// <summary>
         /// Gets or sets the <see cref="ViewDataDictionary"/> for this result.
         /// </summary>
         public ViewDataDictionary ViewData { get; set; }
 
+        /// <summary>
+        /// Gets or sets the <see cref="ITempDataDictionary"/> for this result.
+        /// </summary>
+        public ITempDataDictionary TempData { get; set; }
+
         /// <summary>
         /// Gets or sets the <see cref="IViewEngine"/> used to locate views.
         /// </summary>
@@ -58,6 +58,11 @@ namespace Microsoft.AspNetCore.Mvc
         /// <c>ActionContext.HttpContext.RequestServices</c> is used.</remarks>
         public IViewEngine ViewEngine { get; set; }
 
+        /// <summary>
+        /// Gets or sets the Content-Type header for the response.
+        /// </summary>
+        public string ContentType { get; set; }
+
         /// <inheritdoc />
         public override Task ExecuteResultAsync(ActionContext context)
         {

test/Microsoft.AspNetCore.Mvc.ViewFeatures.Test/ControllerUnitTestabilityTests.cs

@@ -34,15 +34,10 @@ namespace Microsoft.AspNetCore.Mvc
             var viewResult = Assert.IsType<ViewResult>(result);
             Assert.Equal(viewName, viewResult.ViewName);
             Assert.NotNull(viewResult.ViewData);
+            Assert.Same(model, viewResult.Model);
             Assert.Same(model, viewResult.ViewData.Model);
             Assert.Same(controller.ViewData, viewResult.ViewData);
             Assert.Same(controller.TempData, viewResult.TempData);
-
-            if (model != null)
-            {
-                Assert.IsType(model.GetType(), viewResult.ViewData.Model);
-                Assert.NotNull(viewResult.ViewData.Model);
-            }
         }
 
         [Theory]
@@ -61,15 +56,10 @@ namespace Microsoft.AspNetCore.Mvc
             var viewResult = Assert.IsType<PartialViewResult>(result);
             Assert.Equal(viewName, viewResult.ViewName);
             Assert.NotNull(viewResult.ViewData);
+            Assert.Same(model, viewResult.Model);
             Assert.Same(model, viewResult.ViewData.Model);
             Assert.Same(controller.ViewData, viewResult.ViewData);
             Assert.Same(controller.TempData, viewResult.TempData);
-
-            if (model != null)
-            {
-                Assert.IsType(model.GetType(), viewResult.ViewData.Model);
-                Assert.NotNull(viewResult.ViewData.Model);
-            }
         }
 
         [Fact]

test/Microsoft.AspNetCore.Mvc.ViewFeatures.Test/Internal/PartialViewResultTest.cs

@@ -22,6 +22,23 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures.Internal
     // and ViewExecutorTest for more comprehensive tests.
     public class PartialViewResultTest
     {
+        [Fact]
+        public void Model_ExposesViewDataModel()
+        {
+            // Arrange
+            var customModel = new object();
+            var viewResult = new PartialViewResult
+            {
+                ViewData = new ViewDataDictionary(new EmptyModelMetadataProvider())
+                {
+                    Model = customModel
+                },
+            };
+
+            // Act & Assert
+            Assert.Same(customModel, viewResult.Model);
+        }
+
         [Fact]
         public async Task ExecuteResultAsync_Throws_IfViewCouldNotBeFound_MessageUsesGetViewLocations()
         {

test/Microsoft.AspNetCore.Mvc.ViewFeatures.Test/ViewComponentResultTest.cs

@@ -34,6 +34,23 @@ namespace Microsoft.AspNetCore.Mvc
         private readonly ITempDataDictionary _tempDataDictionary =
             new TempDataDictionary(new DefaultHttpContext(), new SessionStateTempDataProvider());
 
+        [Fact]
+        public void Model_ExposesViewDataModel()
+        {
+            // Arrange
+            var customModel = new object();
+            var viewResult = new ViewComponentResult
+            {
+                ViewData = new ViewDataDictionary(new EmptyModelMetadataProvider())
+                {
+                    Model = customModel
+                },
+            };
+
+            // Act & Assert
+            Assert.Same(customModel, viewResult.Model);
+        }
+
         [Fact]
         public async Task ExecuteAsync_ViewComponentResult_AllowsNullViewDataAndTempData()
         {