/** * Gets the name (or names) of the primary key field(s) for the object. * * @return mixed The string (or an array of strings) representing the name(s) * of the primary key field(s) for this instance. */ public function getPK() { if ($this->_pk === null) { $this->_pk = $this->xpdo->getPK($this->_class); } return $this->_pk; }