ServiceStack.OrmLite extension for INSERT INTO ... SELECT

InsertIntoSelect.cs

public static int InsertIntoSelect<TEntity>(this IDbConnection db, ISqlExpression expression) where TEntity : IHasId<int>
{
    var modelDef = typeof(TEntity).GetModelMetadata();
    var untypedExpression = expression.GetUntypedSqlExpression();

    // Tokenize the select list
    var commands = untypedExpression
        .SelectExpression
        .Substring("SELECT ".Length)
        .ParseCommands();

    // Get field names from the tokenized list  
    var fields = commands
        .ToDictionary(k => Regex.Match(k.Name, @"(?>.+ AS )?(?>""?\w+""?.)?""?(\w+)""?").Groups[1].Value, v => v);

    // ToInsertStatement reorders all fields based on Model Metadata order.
    string fullInsertStatement = db.ToInsertStatement(Activator.CreateInstance<TEntity>(), fields.Keys);

    // https://github.com/ServiceStack/ServiceStack.OrmLite/blob/67d57acbc65ab200219b12f5ed7a0ecb8ac19b69/src/ServiceStack.OrmLite/OrmLiteDialectProviderBase.cs#L628
    var reorderedSelectList = new List<string>();
    foreach (var fieldDef in modelDef.FieldDefinitionsArray)
    {
        if (fieldDef.ShouldSkipInsert())
            continue;

        if (fields.ContainsKey(fieldDef.Name))
        {
            reorderedSelectList.Add(fields[fieldDef.Name].Name);
            continue;
        }

        if (fields.ContainsKey(fieldDef.FieldName))
            reorderedSelectList.Add(fields[fieldDef.FieldName].Name);
    }

    // rebuild the select expression using the re-ordered select list
    untypedExpression.SelectExpression = reorderedSelectList
        .Aggregate(new StringBuilder(),
            (sb, f) => sb.AppendFormat("{0},", f),
            sb =>
            {
                sb.Length--; // skip trailing comma
                return $"SELECT {sb.ToString()}";
            });

    // https://github.com/ServiceStack/ServiceStack.OrmLite/blob/67d57acbc65ab200219b12f5ed7a0ecb8ac19b69/src/ServiceStack.OrmLite/Expressions/SqlExpression.cs#L1279
    var sql = expression.ToSelectStatement();
    string selectStatement = db.GetDialectProvider().MergeParamsIntoSql(sql, expression.Params);

    // replace VALUES with the user query
    string insertIntoSelectStatement = Regex.Replace(fullInsertStatement, "VALUES .*$", selectStatement);

    //  
    int rowsAffected = db.ExecuteSql(insertIntoSelectStatement);

    return rowsAffected;
}