code: public String toQueryString(Criteria criteria, CriteriaQueryBuilder queryBuilder) {
      return new StringBuilder()
        .append("DISTINCT ")
        .append( projection.toQueryString(criteria, queryBuilder) )
        .toString();
    }
docs: /*
  @see org.criteria4jpa.projection.Projection#toQueryString(org.criteria4jpa.Criteria, org.criteria4jpa.impl.CriteriaQueryBuilder)