protected override BaseCriteria VisitCriteria(Criteria criteria)
        {
            if (criteria.Expression.IsEmptyOrNull())
                return base.VisitCriteria(criteria);

            if (!SqlSyntax.IsValidIdentifier(criteria.Expression))
                throw new ValidationError("InvalidCriteriaField",
                    String.Format("{0} is not a valid field name!", criteria.Expression));

            return base.VisitCriteria(criteria);
        }
 protected virtual BaseCriteria VisitCriteria(Criteria criteria)
 {
     return criteria;
 }