Make Partial on PageBase and PageModel work correctly

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

@@ -368,6 +368,7 @@ public abstract partial class PageBase : Microsoft.AspNetCore.Mvc.Razor.RazorPag
     {
         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 @@ public abstract partial class PageModel : Microsoft.AspNetCore.Mvc.Filters.IAsyn
     {
         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/test/PageModelTest.cs

@@ -1898,13 +1898,15 @@ public async Task AsyncPageHandlerSelectingMethod_InvokeSyncMethods()
         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 @@ public void PartialView_WithName()
             // 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 @@ public void PartialView_WithNameAndModel()
             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

@@ -1700,36 +1700,42 @@ public void StatusCode_SetsStatusCode()
         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");
 
             // 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 @@ public void PartialView_WithNameAndModel()
             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/Models/TestModel.cs → src/Mvc/samples/MvcSandbox/Pages/PagesHome.cshtml.cs

@@ -6,7 +6,7 @@
 
 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 @@ public async Task Page_Handler_ReturnTypeImplementsIActionResult()
         }
 
         [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/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/_PartialWithModel.cshtml → 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>