Fix: Use MemoryStream as ClrType for complex JSON types

Changed _jsonComplex to use MySqlJsonTypeMapping<MemoryStream> instead of byte[].
This makes the ClrType match what EF Core expects for complex JSON types,
while still reading as string and converting in CustomizeDataReaderExpression.

Updated the condition to check for MemoryStream type instead of non-string.

This should resolve both the coercion error and SQL generation issues because:
- ClrType = MemoryStream matches EF Core's expectations for complex JSON
- Still reads as string from MySQL (GetDataReaderMethod returns GetString)
- Converts string to MemoryStream only when ClrType == MemoryStream
- Regular JSON columns use MySqlJsonTypeMapping<string> with no conversion

Co-authored-by: renemadsen <76994+renemadsen@users.noreply.github.com>

Author: Copilot

src/EFCore.MySql/Storage/Internal/MySqlJsonTypeMapping.cs

@@ -143,13 +143,13 @@ public override MethodInfo GetDataReaderMethod()
         /// <summary>
         /// Customizes the data reader expression for JSON types.
         /// MySQL stores JSON as strings, but EF Core expects MemoryStream for complex JSON types.
-        /// We only convert for non-string CLR types (complex JSON types), not for regular JSON columns mapped to string.
+        /// We only convert when ClrType is MemoryStream (complex JSON types), not for regular JSON columns mapped to string.
         /// </summary>
         public override Expression CustomizeDataReaderExpression(Expression expression)
         {
-            // Only convert for complex JSON types (where ClrType is NOT string)
+            // Only convert for complex JSON types (where ClrType is MemoryStream)
             // For regular JSON columns mapped to string, don't convert
-            if (expression.Type == typeof(string) && ClrType != typeof(string))
+            if (expression.Type == typeof(string) && ClrType == typeof(System.IO.MemoryStream))
             {
                 // Validate that reflection lookups succeeded
                 if (_utf8Property == null || _getBytesMethod == null || _memoryStreamCtor == null)

src/EFCore.MySql/Storage/Internal/MySqlTypeMappingSource.cs

@@ -90,7 +90,7 @@ private readonly RelationalTypeMapping _binaryRowVersion6
         // JSON default mapping
         private MySqlJsonTypeMapping<string> _jsonDefaultString;
         // JSON mapping for complex types (JsonTypePlaceholder)
-        private MySqlJsonTypeMapping<byte[]> _jsonComplex;
+        private MySqlJsonTypeMapping<System.IO.MemoryStream> _jsonComplex;
 
         // Scaffolding type mappings
         private readonly MySqlCodeGenerationMemberAccessTypeMapping _codeGenerationMemberAccess = MySqlCodeGenerationMemberAccessTypeMapping.Default;
@@ -137,7 +137,7 @@ private void Initialize()
                 : null;
 
             _jsonDefaultString = new MySqlJsonTypeMapping<string>("json", null, null, _options.NoBackslashEscapes, _options.ReplaceLineBreaksWithCharFunction);
-            _jsonComplex = new MySqlJsonTypeMapping<byte[]>("json", null, null, _options.NoBackslashEscapes, _options.ReplaceLineBreaksWithCharFunction);
+            _jsonComplex = new MySqlJsonTypeMapping<System.IO.MemoryStream>("json", null, null, _options.NoBackslashEscapes, _options.ReplaceLineBreaksWithCharFunction);
 
             _storeTypeMappings
                 = new Dictionary<string, RelationalTypeMapping[]>(StringComparer.OrdinalIgnoreCase)