public function __construct($value, $field_name, $table_name = NULL, $operator = NULL, $conjunction = NULL, $negated = NULL)
 {
     parent::__construct($field_name, $table_name, $conjunction, $negated);
     $this->value = $value;
     if (isset($operator)) {
         $this->operator = $operator;
     } else {
         $this->operator = '=';
     }
 }
 public function __construct($field_name, $table_name = NULL, $conjunction = NULL, $negated = NULL)
 {
     parent::__construct($field_name, $table_name, $conjunction, $negated);
     $this->values = array();
 }