Check if element type is as requested (#15974)

---------

Co-authored-by: Mike Alhayek <mike@crestapps.com>

src/OrchardCore/OrchardCore.ContentManagement.Abstractions/ContentExtensions.cs

@@ -63,12 +63,14 @@ public static class ContentExtensions
         /// <returns>The content element instance or. <code>null</code> if it doesn't exist.</returns>
         public static ContentElement Get(this ContentElement contentElement, Type contentElementType, string name)
         {
-            if (contentElement.Elements.TryGetValue(name, out var element))
+            if (contentElement.Elements.TryGetValue(name, out var element) &&
+                element.GetType().IsAssignableTo(contentElementType))
             {
                 return element;
             }
 
             var elementData = contentElement.Data[name] as JsonObject;
+
             if (elementData is null)
             {
                 return null;

test/OrchardCore.Tests/ContentManagement/ContentElementTests.cs

@@ -0,0 +1,69 @@
+using System.Text.Json;
+using OrchardCore.ContentManagement;
+using OrchardCore.Title.Models;
+
+namespace OrchardCore.Tests.ContentManagement;
+public class ContentElementTests
+{
+    [Fact]
+    public void Get_WhenCastingBaseTypeThenConcreteType_ReturnNewInstance()
+    {
+        var contentItem = new ContentItem();
+        var titlePart = new TitlePart
+        {
+            Title = "test"
+        };
+
+        contentItem.Weld(titlePart);
+
+        var json = JConvert.SerializeObject(contentItem);
+
+        var contentItem2 = JConvert.DeserializeObject<ContentItem>(json);
+
+        // act
+        // The order arrangement of the next two calls are important.
+        // First cast to ContentPart.
+        var contentPart = contentItem2.Get<ContentPart>(nameof(TitlePart));
+
+        // Second, cast to TitlePart.
+        var actualPart = contentItem2.Get<TitlePart>(nameof(TitlePart));
+
+        // assert
+        Assert.NotNull(contentPart);
+        Assert.NotNull(actualPart);
+
+        // actualPart should deserialized again, so it must not be same as contentPart.
+        Assert.NotSame(contentPart, actualPart);
+    }
+
+    [Fact]
+    public void Get_WhenCastingConcreteTypeThenBaseType_ReturnNewInstance()
+    {
+        var contentItem = new ContentItem();
+        var titlePart = new TitlePart
+        {
+            Title = "test"
+        };
+
+        contentItem.Weld(titlePart);
+
+        var json = JConvert.SerializeObject(contentItem);
+
+        var contentItem2 = JConvert.DeserializeObject<ContentItem>(json);
+
+        // act
+        // The order arrangement of the next two calls are important.
+        // First cast to TitlePart.
+        var actualPart = contentItem2.Get<TitlePart>(nameof(TitlePart));
+
+        // Second, cast to ContentPart.
+        var contentPart = contentItem2.Get<ContentPart>(nameof(TitlePart));
+
+        // assert
+        Assert.NotNull(contentPart);
+        Assert.NotNull(actualPart);
+
+        // contentPart should be returned from cache, so it must be same as actualPart.
+        Assert.Same(contentPart, actualPart);
+    }
+}