yii\mongodb\ActiveRecord::deleteInternal PHP Method

    protected function deleteInternal()
    {
        // we do not check the return value of deleteAll() because it's possible
        // the record is already deleted in the database and thus the method will return 0
        $condition = $this->getOldPrimaryKey(true);
        $lock = $this->optimisticLock();
        if ($lock !== null) {
            $condition[$lock] = $this->{$lock};
        }
        $result = static::getCollection()->remove($condition);
        if ($lock !== null && !$result) {
            throw new StaleObjectException('The object being deleted is outdated.');
        }
        $this->setOldAttributes(null);
        return $result;
    }