Make Partial on PageBase and PageModel work correctly (#13013)

* Make Partial on PageBase and PageModel work correctly

Fixes https://github.com/aspnet/AspNetCore/issues/10438

src/Mvc/Mvc.RazorPages/ref/Microsoft.AspNetCore.Mvc.RazorPages.netcoreapp3.0.cs

@@ -368,6 +368,7 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages
     {
         protected PageBase() { }
         public Microsoft.AspNetCore.Http.HttpContext HttpContext { get { throw null; } }
+        public Microsoft.AspNetCore.Mvc.ModelBinding.IModelMetadataProvider MetadataProvider { get { throw null; } set { } }
         public Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateDictionary ModelState { get { throw null; } }
         public Microsoft.AspNetCore.Mvc.RazorPages.PageContext PageContext { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute]set { } }
         public Microsoft.AspNetCore.Http.HttpRequest Request { get { throw null; } }
@@ -500,6 +501,7 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages
     {
         protected PageModel() { }
         public Microsoft.AspNetCore.Http.HttpContext HttpContext { get { throw null; } }
+        public Microsoft.AspNetCore.Mvc.ModelBinding.IModelMetadataProvider MetadataProvider { get { throw null; } set { } }
         public Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateDictionary ModelState { get { throw null; } }
         [Microsoft.AspNetCore.Mvc.RazorPages.PageContextAttribute]
         public Microsoft.AspNetCore.Mvc.RazorPages.PageContext PageContext { get { throw null; } set { } }

src/Mvc/Mvc.RazorPages/src/PageBase.cs

@@ -13,6 +13,7 @@ using Microsoft.AspNetCore.Mvc.ModelBinding;
 using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
 using Microsoft.AspNetCore.Mvc.Razor;
 using Microsoft.AspNetCore.Mvc.Rendering;
+using Microsoft.AspNetCore.Mvc.ViewFeatures;
 using Microsoft.AspNetCore.Routing;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Net.Http.Headers;
@@ -61,6 +62,19 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages
         /// </summary>
         public ModelStateDictionary ModelState => PageContext?.ModelState;
 
+        /// <summary>
+        /// Gets or sets the <see cref="IModelMetadataProvider"/>.
+        /// </summary>
+        public IModelMetadataProvider MetadataProvider
+        {
+            get
+            {
+                _metadataProvider ??= HttpContext?.RequestServices?.GetRequiredService<IModelMetadataProvider>();
+                return _metadataProvider;
+            }
+            set => _metadataProvider = value ?? throw new ArgumentNullException(nameof(value));
+        }
+
         private IObjectModelValidator ObjectValidator
         {
             get
@@ -74,19 +88,6 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages
             }
         }
 
-        private IModelMetadataProvider MetadataProvider
-        {
-            get
-            {
-                if (_metadataProvider == null)
-                {
-                    _metadataProvider = HttpContext?.RequestServices?.GetRequiredService<IModelMetadataProvider>();
-                }
-
-                return _metadataProvider;
-            }
-        }
-
         private IModelBinderFactory ModelBinderFactory
         {
             get
@@ -1206,12 +1207,17 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages
         /// <returns>The created <see cref="PartialViewResult"/> object for the response.</returns>
         public virtual PartialViewResult Partial(string viewName, object model)
         {
-            ViewContext.ViewData.Model = model;
+            // ViewContext.ViewData is an instance of ViewDataDictionary<MyPageModel>, but we need an instance
+            // of ViewDataDictionary<MyPartialViewModel>.
+            var viewData = new ViewDataDictionary(MetadataProvider, ViewContext.ViewData.ModelState)
+            {
+                Model = model,
+            };
 
             return new PartialViewResult
             {
                 ViewName = viewName,
-                ViewData = ViewContext.ViewData
+                ViewData = viewData
             };
         }
 

src/Mvc/Mvc.RazorPages/src/PageModel.cs

@@ -139,6 +139,19 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages
             }
         }
 
+        /// <summary>
+        /// Gets or sets the <see cref="IModelMetadataProvider"/>.
+        /// </summary>
+        public IModelMetadataProvider MetadataProvider
+        {
+            get
+            {
+                _metadataProvider ??= HttpContext?.RequestServices?.GetRequiredService<IModelMetadataProvider>();
+                return _metadataProvider;
+            }
+            set => _metadataProvider = value ?? throw new ArgumentNullException(nameof(value));
+        }
+
         /// <summary>
         /// Gets the <see cref="ViewDataDictionary"/>.
         /// </summary>
@@ -157,19 +170,6 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages
             }
         }
 
-        private IModelMetadataProvider MetadataProvider
-        {
-            get
-            {
-                if (_metadataProvider == null)
-                {
-                    _metadataProvider = HttpContext?.RequestServices?.GetRequiredService<IModelMetadataProvider>();
-                }
-
-                return _metadataProvider;
-            }
-        }
-
         private IModelBinderFactory ModelBinderFactory
         {
             get
@@ -1631,12 +1631,18 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages
         /// <returns>The created <see cref="PartialViewResult"/> object for the response.</returns>
         public virtual PartialViewResult Partial(string viewName, object model)
         {
-            ViewData.Model = model;
+            // PageModel.ViewData is an instance of ViewDataDictionary<MyPageModel>, but we need an instance
+            // of ViewDataDictionary<MyPartialViewModel>.
+
+            var viewData = new ViewDataDictionary(MetadataProvider, ViewData.ModelState)
+            {
+                Model = model,
+            };
 
             return new PartialViewResult
             {
                 ViewName = viewName,
-                ViewData = ViewData
+                ViewData = viewData
             };
         }
 

src/Mvc/Mvc.RazorPages/test/PageModelTest.cs

@@ -1898,13 +1898,15 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages
         public void PartialView_WithName()
         {
             // Arrange
-            var viewData = new ViewDataDictionary(new EmptyModelMetadataProvider(), new ModelStateDictionary());
+            var modelMetadataProvider = new EmptyModelMetadataProvider();
+            var viewData = new ViewDataDictionary(modelMetadataProvider, new ModelStateDictionary());
             var pageModel = new TestPageModel
             {
                 PageContext = new PageContext
                 {
                     ViewData = viewData
-                }
+                },
+                MetadataProvider = modelMetadataProvider,
             };
 
             // Act
@@ -1913,20 +1915,22 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages
             // Assert
             Assert.NotNull(result);
             Assert.Equal("LoginStatus", result.ViewName);
-            Assert.Same(viewData, result.ViewData);
+            Assert.Null(result.Model);
         }
 
         [Fact]
         public void PartialView_WithNameAndModel()
         {
             // Arrange
-            var viewData = new ViewDataDictionary(new EmptyModelMetadataProvider(), new ModelStateDictionary());
+            var modelMetadataProvider = new EmptyModelMetadataProvider();
+            var viewData = new ViewDataDictionary(modelMetadataProvider, new ModelStateDictionary());
             var pageModel = new TestPageModel
             {
                 PageContext = new PageContext
                 {
                     ViewData = viewData
-                }
+                },
+                MetadataProvider = modelMetadataProvider,
             };
             var model = new { Username = "Admin" };
 
@@ -1937,7 +1941,6 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages
             Assert.NotNull(result);
             Assert.Equal("LoginStatus", result.ViewName);
             Assert.Equal(model, result.Model);
-            Assert.Same(viewData, result.ViewData);
         }
 
         [Fact]

src/Mvc/Mvc.RazorPages/test/PageTest.cs

@@ -1700,14 +1700,17 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages
         public void PartialView_WithName()
         {
             // Arrange
-            var viewData = new ViewDataDictionary(new EmptyModelMetadataProvider(), new ModelStateDictionary());
+            var modelMetadataProvider = new EmptyModelMetadataProvider();
+            var viewData = new ViewDataDictionary(modelMetadataProvider, new ModelStateDictionary());
             var pageModel = new TestPage
             {
                 ViewContext = new ViewContext
                 {
                     ViewData = viewData
-                }
+                },
+                MetadataProvider = modelMetadataProvider,
             };
+            viewData.Model = pageModel;
 
             // Act
             var result = pageModel.Partial("LoginStatus");
@@ -1715,21 +1718,24 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages
             // Assert
             Assert.NotNull(result);
             Assert.Equal("LoginStatus", result.ViewName);
-            Assert.Same(viewData, result.ViewData);
+            Assert.Null(result.Model);
         }
 
         [Fact]
         public void PartialView_WithNameAndModel()
         {
             // Arrange
-            var viewData = new ViewDataDictionary(new EmptyModelMetadataProvider(), new ModelStateDictionary());
+            var modelMetadataProvider = new EmptyModelMetadataProvider();
+            var viewData = new ViewDataDictionary(modelMetadataProvider, new ModelStateDictionary());
             var pageModel = new TestPage
             {
                 ViewContext = new ViewContext
                 {
                     ViewData = viewData
-                }
+                },
+                MetadataProvider = modelMetadataProvider,
             };
+            viewData.Model = pageModel;
             var model = new { Username = "Admin" };
 
             // Act
@@ -1739,7 +1745,6 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages
             Assert.NotNull(result);
             Assert.Equal("LoginStatus", result.ViewName);
             Assert.Equal(model, result.Model);
-            Assert.Same(viewData, result.ViewData);
         }
 
         [Fact]

src/Mvc/samples/MvcSandbox/Pages/PagesHome.cshtml

@@ -1,5 +1,5 @@
 @page
-@model TestModel
+@model PagesHome
 @{
 
     ViewData["Title"] = "Hello from pages";

src/Mvc/samples/MvcSandbox/Pages/PagesHome.cshtml.cs

@@ -6,7 +6,7 @@ using Microsoft.AspNetCore.Mvc.RazorPages;
 
 namespace MvcSandbox
 {
-    public class TestModel : PageModel
+    public class PagesHome : PageModel
     {
         public string Name { get; private set; } = "World";
 

src/Mvc/test/Mvc.FunctionalTests/RazorPagesTest.cs

@@ -144,23 +144,43 @@ namespace Microsoft.AspNetCore.Mvc.FunctionalTests
         }
 
         [Fact]
-        public async Task Page_Handler_ReturnPartialWithoutModel()
+        public async Task PageWithoutModel_ReturnPartial()
         {
             // Act
-            var document = await Client.GetHtmlDocumentAsync("RenderPartialWithoutModel");
+            using var document = await Client.GetHtmlDocumentAsync("PageWithoutModelRenderPartial");
 
             var element = document.RequiredQuerySelector("#content");
-            Assert.Equal("Welcome, Guest", element.TextContent);
+            Assert.Equal("Hello from Razor Page", element.TextContent);
         }
 
         [Fact]
-        public async Task Page_Handler_ReturnPartialWithModel()
+        public async Task PageWithModel_Works()
         {
             // Act
-            var document = await Client.GetHtmlDocumentAsync("RenderPartialWithModel");
+            using var document = await Client.GetHtmlDocumentAsync("RenderPartial");
 
             var element = document.RequiredQuerySelector("#content");
-            Assert.Equal("Welcome, Admin", element.TextContent);
+            Assert.Equal("Hello from RenderPartialModel", element.TextContent);
+        }
+
+        [Fact]
+        public async Task PageWithModel_PartialUsingPageModelWorks()
+        {
+            // Act
+            using var document = await Client.GetHtmlDocumentAsync("RenderPartial/UsePageModelAsPartialModel");
+
+            var element = document.RequiredQuerySelector("#content");
+            Assert.Equal("Hello from RenderPartialWithModel", element.TextContent);
+        }
+
+        [Fact]
+        public async Task PageWithModel_PartialWithNoModel()
+        {
+            // Act
+            using var document = await Client.GetHtmlDocumentAsync("RenderPartial/NoPartialModel");
+
+            var element = document.RequiredQuerySelector("#content");
+            Assert.Equal("Hello default", element.TextContent);
         }
 
         [Fact]

src/Mvc/test/WebSites/RazorPagesWebSite/Models/RenderPartialModel.cs

@@ -0,0 +1,10 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+namespace RazorPagesWebSite.Models
+{
+    public class RenderPartialModel
+    {
+        public string Value { get; set; }
+    }
+}

src/Mvc/test/WebSites/RazorPagesWebSite/PageWithoutModelRenderPartial.cshtml

@@ -0,0 +1,6 @@
+@page
+@using RazorPagesWebSite.Models
+
+@functions {
+    public IActionResult OnGet() => Partial("_RenderPartial", new RenderPartialModel { Value = "Hello from Razor Page" });
+}

src/Mvc/test/WebSites/RazorPagesWebSite/RenderPartial.cshtml

@@ -0,0 +1,7 @@
+@page "{handler?}"
+@model RazorPagesWebSite.RenderPartialWithModel
+
+@{ 
+    throw new Exception("This should not be called");
+
+}

src/Mvc/test/WebSites/RazorPagesWebSite/RenderPartial.cshtml.cs

@@ -0,0 +1,20 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.Mvc.RazorPages;
+using RazorPagesWebSite.Models;
+
+namespace RazorPagesWebSite
+{
+    public class RenderPartialWithModel : PageModel
+    {
+        public string Text { get; set; } = $"Hello from {nameof(RenderPartialWithModel)}";
+
+        public IActionResult OnGet() => Partial("_RenderPartial", new RenderPartialModel { Value = $"Hello from {nameof(RenderPartialModel)}" });
+
+        public IActionResult OnGetUsePageModelAsPartialModel() => Partial("_RenderPartialPageModel", this);
+
+        public IActionResult OnGetNoPartialModel() => Partial("_RenderPartial");
+    }
+}

src/Mvc/test/WebSites/RazorPagesWebSite/RenderPartialWithModel.cs

@@ -1,15 +0,0 @@
-// Copyright (c) .NET Foundation. All rights reserved.
-// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
-
-using Microsoft.AspNetCore.Mvc;
-using Microsoft.AspNetCore.Mvc.RazorPages;
-
-namespace RazorPagesWebSite
-{
-    public class RenderPartialWithModel : PageModel
-    {
-        public IActionResult OnGet() => Partial("_PartialWithModel", this);
-
-        public string Username => "Admin";
-    }
-}

src/Mvc/test/WebSites/RazorPagesWebSite/RenderPartialWithModel.cshtml

@@ -1,4 +0,0 @@
-@page
-@model RazorPagesWebSite.RenderPartialWithModel
-
-<p>The partial will be loaded here ...</p>

src/Mvc/test/WebSites/RazorPagesWebSite/RenderPartialWithoutModel.cshtml

@@ -1,5 +0,0 @@
-@page
-
-@functions {
-    public IActionResult OnGet() => Partial("_PartialWithoutModel");
-}

src/Mvc/test/WebSites/RazorPagesWebSite/Views/Shared/_PartialWithoutModel.cshtml

@@ -1 +0,0 @@
-<span id="content">Welcome, Guest</span>

src/Mvc/test/WebSites/RazorPagesWebSite/Views/Shared/_RenderPartial.cshtml

@@ -0,0 +1,4 @@
+@using RazorPagesWebSite.Models
+@model RenderPartialModel
+
+<span id="content">@(Model?.Value ?? "Hello default")</span>

src/Mvc/test/WebSites/RazorPagesWebSite/Views/Shared/_RenderPartialPageModel.cshtml

@@ -1,3 +1,3 @@
 @model RazorPagesWebSite.RenderPartialWithModel
 
-<span id="content">Welcome, @Model.Username</span>
+<span id="content">@Model.Text</span>