yii\db\ActiveRecord::primaryKey PHP Метод

    public static function primaryKey()
    {
        return static::getTableSchema()->primaryKey;
    }

 protected function loadExisting()
 {
     $pk = [];
     foreach ($this->_attributes as $attribute) {
         if (in_array($attribute->standardAttribute->name, $this->_instance->primaryKey())) {
             $pk[$attribute->standardAttribute->name] = $attribute->value;
         }
     }
     if (!$pk) {
         return;
     }
     if (count($pk) == 1 && !reset($pk)) {
         return;
     }
     foreach ($pk as $value) {
         if (!$value) {
             throw new RowException($this->row, 'For updated model all primary key attributes must be specified.');
         }
     }
     /* @var $modelClass \yii\db\ActiveRecord */
     $modelClass = $this->_standardModel->className;
     $model = $modelClass::findOne($pk);
     if (!$model) {
         throw new RowException($this->row, 'Model for update not found.');
     }
     $this->_instance = $model;
 }