protected override DbExpression VisitListExpression(DbListExpression listExpression)
{
if (listExpression.Count() == 0)
return ExpressionFactory.Sql(string.Empty);
//var syntax = listExpression.Select(e => Visit(e)).Aggregate((current, next) => current + "," + next);
var syntax = listExpression.Select(e => Visit(e).ToString()).Aggregate((current, next) => current + "," + next);
return ExpressionFactory.Sql(syntax);
}