Debug: Add more SQL generation logging

Added:
- GenerateSqlLiteral and GenerateProviderValueSqlLiteral logging in MySqlComplexJsonTypeMapping
- MySqlCommandInterceptor class to log all SQL commands being executed

This will help capture the actual malformed SQL queries that are causing
syntax errors like "near ', ,'" to diagnose why column projections are empty.

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

Author: Copilot

src/EFCore.MySql/Diagnostics/MySqlCommandInterceptor.cs

@@ -0,0 +1,61 @@
+// Copyright (c) Pomelo Foundation. All rights reserved.
+// Licensed under the MIT. See LICENSE in the project root for license information.
+
+using System;
+using System.Data.Common;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.EntityFrameworkCore.Diagnostics;
+
+namespace Pomelo.EntityFrameworkCore.MySql.Diagnostics
+{
+    /// <summary>
+    /// Debug interceptor to log SQL commands
+    /// </summary>
+    public class MySqlCommandInterceptor : DbCommandInterceptor
+    {
+        public override InterceptionResult<DbDataReader> ReaderExecuting(
+            DbCommand command,
+            CommandEventData eventData,
+            InterceptionResult<DbDataReader> result)
+        {
+            Console.WriteLine($"[DEBUG SQL] Executing command:");
+            Console.WriteLine($"[DEBUG SQL] {command.CommandText}");
+            Console.WriteLine($"[DEBUG SQL] Parameters: {command.Parameters.Count}");
+            return base.ReaderExecuting(command, eventData, result);
+        }
+
+        public override ValueTask<InterceptionResult<DbDataReader>> ReaderExecutingAsync(
+            DbCommand command,
+            CommandEventData eventData,
+            InterceptionResult<DbDataReader> result,
+            CancellationToken cancellationToken = default)
+        {
+            Console.WriteLine($"[DEBUG SQL] Executing command async:");
+            Console.WriteLine($"[DEBUG SQL] {command.CommandText}");
+            Console.WriteLine($"[DEBUG SQL] Parameters: {command.Parameters.Count}");
+            return base.ReaderExecutingAsync(command, eventData, result, cancellationToken);
+        }
+
+        public override InterceptionResult<int> NonQueryExecuting(
+            DbCommand command,
+            CommandEventData eventData,
+            InterceptionResult<int> result)
+        {
+            Console.WriteLine($"[DEBUG SQL NonQuery] Executing command:");
+            Console.WriteLine($"[DEBUG SQL NonQuery] {command.CommandText}");
+            return base.NonQueryExecuting(command, eventData, result);
+        }
+
+        public override ValueTask<InterceptionResult<int>> NonQueryExecutingAsync(
+            DbCommand command,
+            CommandEventData eventData,
+            InterceptionResult<int> result,
+            CancellationToken cancellationToken = default)
+        {
+            Console.WriteLine($"[DEBUG SQL NonQuery] Executing command async:");
+            Console.WriteLine($"[DEBUG SQL NonQuery] {command.CommandText}");
+            return base.NonQueryExecutingAsync(command, eventData, result, cancellationToken);
+        }
+    }
+}

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

@@ -102,6 +102,22 @@ public override Expression CustomizeDataReaderExpression(Expression expression)
             Console.WriteLine($"[DEBUG] MySqlComplexJsonTypeMapping: No conversion, calling base.CustomizeDataReaderExpression");
             return base.CustomizeDataReaderExpression(expression);
         }
+
+        public override string GenerateSqlLiteral(object value)
+        {
+            Console.WriteLine($"[DEBUG] MySqlComplexJsonTypeMapping.GenerateSqlLiteral called - value type: {value?.GetType()?.Name ?? "null"}");
+            var result = base.GenerateSqlLiteral(value);
+            Console.WriteLine($"[DEBUG] MySqlComplexJsonTypeMapping.GenerateSqlLiteral result: {result}");
+            return result;
+        }
+
+        public override string GenerateProviderValueSqlLiteral(object value)
+        {
+            Console.WriteLine($"[DEBUG] MySqlComplexJsonTypeMapping.GenerateProviderValueSqlLiteral called - value type: {value?.GetType()?.Name ?? "null"}");
+            var result = base.GenerateProviderValueSqlLiteral(value);
+            Console.WriteLine($"[DEBUG] MySqlComplexJsonTypeMapping.GenerateProviderValueSqlLiteral result: {result}");
+            return result;
+        }
     }
 
     public class MySqlJsonTypeMapping<T> : MySqlJsonTypeMapping