protected function _tagExists($tag) {
		$tagsTable = $this->_table->{$this->getConfig('tagsAlias')}->getTarget();
		$result = $tagsTable->find()
			->where([
				$tagsTable->aliasField('slug') => $tag,
			])
			->select([
				$tagsTable->aliasField($tagsTable->getPrimaryKey())
			])
			->first();
		if (!empty($result)) {
			return $result->id;
		}
		return null;
	}