/**
  * filter
  *
  * Apply the query filter
  * 
  * @param  \Doctrine\MongoDB\Query\Builder $qb
  * @return \Doctrine\MongoDB\Query\Expr $expr
  */
 public function filter(Query\Builder $qb)
 {
     $qb->sort($this->fieldName, $this->fieldValue);
     if (null !== $this->spec) {
         return $this->spec->filter($qb);
     }
 }
 /**
  * filter
  *
  * Perform the filter on the query builder
  *
  * @param  \Doctrine\MongoDB\Query $qb
  * @return \Doctrine\MongoDB\Query\Expr
  */
 public function filter(Query\Builder $qb)
 {
     return $this->spec->filter($qb);
 }