Fix to #32192 - Remove lookup of JsonTypeMapping via JsonElement

When adding support for JSON mapped types, we decided to use JsonElement as a CLR type marker for JsonTypeMapping. This decision was in hindsight incorrect, it makes it hard for providers that actually support weak-typed json (npgsql) and throws cryptic exception (No coercion operator is defined between types 'System.IO.MemoryStream' and 'System.Text.Json.JsonElement) for providers that don't support it, when customers try to do it regardless.
Fix is to create a dummy type and use that instead, so JsonElement is no longer recognized by base EFCore.

Fixes #32192
also fixes #34752

Author: maumar

Diff for: src/EFCore.Relational/Metadata/Internal/JsonColumn.cs

@@ -36,7 +36,7 @@ public JsonColumn(
     ///     doing so can result in application failures when updating to a new Entity Framework Core release.
     /// </summary>
     protected override RelationalTypeMapping GetDefaultStoreTypeMapping()
-        => (RelationalTypeMapping)Table.Model.Model.GetModelDependencies().TypeMappingSource.FindMapping(typeof(JsonElement))!;
+        => (RelationalTypeMapping)Table.Model.Model.GetModelDependencies().TypeMappingSource.FindMapping(typeof(JsonClrType))!;
 
     /// <summary>
     ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to

Diff for: src/EFCore.Relational/Metadata/Internal/JsonColumnBase.cs

@@ -36,5 +36,5 @@ public JsonColumnBase(
     ///     doing so can result in application failures when updating to a new Entity Framework Core release.
     /// </summary>
     protected override RelationalTypeMapping GetDefaultStoreTypeMapping()
-        => (RelationalTypeMapping)Table.Model.Model.GetModelDependencies().TypeMappingSource.FindMapping(typeof(JsonElement))!;
+        => (RelationalTypeMapping)Table.Model.Model.GetModelDependencies().TypeMappingSource.FindMapping(typeof(JsonClrType))!;
 }

Diff for: src/EFCore.Relational/Metadata/Internal/JsonViewColumn.cs

@@ -36,5 +36,5 @@ public JsonViewColumn(
     ///     doing so can result in application failures when updating to a new Entity Framework Core release.
     /// </summary>
     protected override RelationalTypeMapping GetDefaultStoreTypeMapping()
-        => (RelationalTypeMapping)Table.Model.Model.GetModelDependencies().TypeMappingSource.FindMapping(typeof(JsonElement))!;
+        => (RelationalTypeMapping)Table.Model.Model.GetModelDependencies().TypeMappingSource.FindMapping(typeof(JsonClrType))!;
 }

Diff for: src/EFCore.Relational/Metadata/Internal/RelationalModel.cs

@@ -582,7 +582,7 @@ private static void CreateContainerColumn<TColumnMappingBase>(
         {
             Check.DebugAssert(tableBase.FindColumn(containerColumnName) == null, $"Table does not have column '{containerColumnName}'.");
 
-            var jsonColumnTypeMapping = relationalTypeMappingSource.FindMapping(typeof(JsonElement), storeTypeName: containerColumnType)!;
+            var jsonColumnTypeMapping = relationalTypeMappingSource.FindMapping(typeof(JsonClrType), storeTypeName: containerColumnType)!;
             var jsonColumn = createColumn(containerColumnName, containerColumnType, tableBase, jsonColumnTypeMapping);
             tableBase.Columns.Add(containerColumnName, jsonColumn);
             jsonColumn.IsNullable = !ownership.IsRequiredDependent || !ownership.IsUnique;

Diff for: src/EFCore.Relational/Metadata/JsonClrType.cs

@@ -0,0 +1,11 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace Microsoft.EntityFrameworkCore.Metadata;
+
+/// <summary>
+/// A type representing CLR type of the JsonTypeMapping.
+/// </summary>
+public class JsonClrType
+{
+}

Diff for: src/EFCore.Relational/Storage/JsonTypeMapping.cs

@@ -2,13 +2,12 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Data;
-using System.Text.Json;
 
 namespace Microsoft.EntityFrameworkCore.Storage;
 
 /// <summary>
 ///     <para>
-///         Represents the mapping between a <see cref="JsonElement" /> type and a database type.
+///         Represents the mapping between a JSON object and a database type.
 ///     </para>
 ///     <para>
 ///         This type is typically used by database providers (and other extensions). It is generally

Diff for: src/EFCore.SqlServer/Storage/Internal/SqlServerOwnedJsonTypeMapping.cs

@@ -45,7 +45,7 @@ private static readonly MethodInfo GetStringMethod
     ///     doing so can result in application failures when updating to a new Entity Framework Core release.
     /// </summary>
     public SqlServerOwnedJsonTypeMapping(string storeType)
-        : base(storeType, typeof(JsonElement), System.Data.DbType.String)
+        : base(storeType, typeof(JsonClrType), System.Data.DbType.String)
     {
     }
 

Diff for: src/EFCore.SqlServer/Storage/Internal/SqlServerTypeMappingSource.cs

@@ -3,7 +3,6 @@
 
 using System.Collections;
 using System.Data;
-using System.Text.Json;
 
 namespace Microsoft.EntityFrameworkCore.SqlServer.Storage.Internal;
 
@@ -239,7 +238,7 @@ public SqlServerTypeMappingSource(
         var clrType = mappingInfo.ClrType;
         var storeTypeName = mappingInfo.StoreTypeName;
 
-        if (clrType == typeof(JsonElement))
+        if (clrType == typeof(JsonClrType))
         {
             return storeTypeName == "json"
                 ? SqlServerOwnedJsonTypeMapping.OwnedJsonTypeDefault

Diff for: src/EFCore.Sqlite.Core/Storage/Internal/SqliteJsonTypeMapping.cs

@@ -39,7 +39,7 @@ private static readonly ConstructorInfo MemoryStreamConstructor
     /// </summary>
     /// <param name="storeType">The name of the database type.</param>
     public SqliteJsonTypeMapping(string storeType)
-        : base(storeType, typeof(JsonElement), System.Data.DbType.String)
+        : base(storeType, typeof(JsonClrType), System.Data.DbType.String)
     {
     }
 

Diff for: src/EFCore.Sqlite.Core/Storage/Internal/SqliteTypeMappingSource.cs

@@ -83,7 +83,7 @@ private static readonly HashSet<string> SpatialiteTypes
         { typeof(double), Real },
         { typeof(float), new FloatTypeMapping(RealTypeName) },
         { typeof(Guid), SqliteGuidTypeMapping.Default },
-        { typeof(JsonElement), SqliteJsonTypeMapping.Default }
+        { typeof(JsonClrType), SqliteJsonTypeMapping.Default }
     };
 
     private readonly Dictionary<string, RelationalTypeMapping> _storeTypeMappings = new(StringComparer.OrdinalIgnoreCase)

Diff for: test/EFCore.Relational.Specification.Tests/Query/AdHocMiscellaneousQueryRelationalTestBase.cs

@@ -4,6 +4,7 @@
 #nullable disable
 
 using System.ComponentModel.DataAnnotations.Schema;
+using System.Text.Json;
 using NameSpace1;
 
 namespace Microsoft.EntityFrameworkCore.Query
@@ -239,6 +240,32 @@ public static DateTime Modify(DateTime date)
 
         #endregion
 
+        #region 34752
+
+        [ConditionalFact]
+        public virtual async Task Mapping_JsonElement_property_throws_a_meaningful_exception()
+        {
+            var message = (await Assert.ThrowsAsync<InvalidOperationException>(
+                () => InitializeAsync<Context34752>())).Message;
+
+            Assert.Equal(
+                CoreStrings.PropertyNotAdded(nameof(Context34752.Entity), nameof(Context34752.Entity.Json), nameof(JsonElement)),
+                message);
+        }
+
+        protected class Context34752(DbContextOptions options) : DbContext(options)
+        {
+            public DbSet<Entity> Entities { get; set; }
+
+            public class Entity
+            {
+                public int Id { get; set; }
+                public JsonElement Json { get; set; }
+            }
+        }
+
+        #endregion
+
         #region Inlined redacting
 
         protected abstract DbContextOptionsBuilder SetTranslateParameterizedCollectionsToConstants(DbContextOptionsBuilder optionsBuilder);
@@ -289,6 +316,7 @@ public class TestEntity
         public static readonly IEnumerable<object[]> InlinedRedactingData = [[true, true], [true, false], [false, true], [false, false]];
 
         #endregion
+
     }
 }
 

Diff for: test/EFCore.SqlServer.FunctionalTests/Scaffolding/Baselines/BigModel_with_JSON_columns/DbContextModelBuilder.cs

@@ -1,7 +1,6 @@
 // <auto-generated />
 using System;
 using System.Collections.Generic;
-using System.Text.Json;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.EntityFrameworkCore.Infrastructure;
 using Microsoft.EntityFrameworkCore.Metadata;
@@ -2258,10 +2257,10 @@ private IRelationalModel CreateRelationalModel()
                 IsNullable = true
             };
             principalBaseTable.Columns.Add("ManyOwned", manyOwnedColumn);
-            manyOwnedColumn.Accessors = ColumnAccessorsFactory.CreateGeneric<JsonElement>(manyOwnedColumn);
+            manyOwnedColumn.Accessors = ColumnAccessorsFactory.CreateGeneric<JsonClrType>(manyOwnedColumn);
             var ownedColumn = new JsonColumn("Owned", "nvarchar(max)", principalBaseTable);
             principalBaseTable.Columns.Add("Owned", ownedColumn);
-            ownedColumn.Accessors = ColumnAccessorsFactory.CreateGeneric<JsonElement>(ownedColumn);
+            ownedColumn.Accessors = ColumnAccessorsFactory.CreateGeneric<JsonClrType>(ownedColumn);
             var refTypeArrayColumn = new Column("RefTypeArray", "nvarchar(max)", principalBaseTable)
             {
                 IsNullable = true

Diff for: test/EFCore.Sqlite.FunctionalTests/Scaffolding/Baselines/BigModel_with_JSON_columns/DbContextModelBuilder.cs

@@ -1,7 +1,6 @@
 // <auto-generated />
 using System;
 using System.Collections.Generic;
-using System.Text.Json;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.EntityFrameworkCore.Infrastructure;
 using Microsoft.EntityFrameworkCore.Metadata;
@@ -2325,10 +2324,10 @@ private IRelationalModel CreateRelationalModel()
                 IsNullable = true
             };
             principalBaseTable.Columns.Add("ManyOwned", manyOwnedColumn);
-            manyOwnedColumn.Accessors = ColumnAccessorsFactory.CreateGeneric<JsonElement>(manyOwnedColumn);
+            manyOwnedColumn.Accessors = ColumnAccessorsFactory.CreateGeneric<JsonClrType>(manyOwnedColumn);
             var ownedColumn = new JsonColumn("Owned", "TEXT", principalBaseTable);
             principalBaseTable.Columns.Add("Owned", ownedColumn);
-            ownedColumn.Accessors = ColumnAccessorsFactory.CreateGeneric<JsonElement>(ownedColumn);
+            ownedColumn.Accessors = ColumnAccessorsFactory.CreateGeneric<JsonClrType>(ownedColumn);
             var pointColumn0 = new Column("Point", "geometry", principalBaseTable)
             {
                 IsNullable = true