/**
  * @param QOM\AndInterface $constraint
  *
  * @return string
  */
 public function walkAndConstraint(QOM\AndInterface $constraint)
 {
     return "(" . $this->walkConstraint($constraint->getConstraint1()) . " AND " . $this->walkConstraint($constraint->getConstraint2()) . ")";
 }
 private function walkAndConstraint(QOM\AndInterface $constraint)
 {
     $left = $this->walkConstraint($constraint->getConstraint1());
     $right = $this->walkConstraint($constraint->getConstraint2());
     return sprintf('(%s AND %s)', $left, $right);
 }