public function addAttrCondition($attr) {
        if(!isset($this->_subscription->subject)){
            $this->_subscription->subject = (object) [];
        }

        if(!isset($this->_subscription->subject->condition)){
            $this->_subscription->subject->condition = (object) [];
        }

        if (!isset($this->_subscription->subject->condition->attrs)) {
            $this->_subscription->subject->condition->attrs = [];
        }
        array_push($this->_subscription->subject->condition->attrs, $attr);
        return $this;
    }