FOF30\Model\TreeModel::insertAsFirstChildOf PHP Method

    public function insertAsFirstChildOf(TreeModel &$parentNode)
    {
        if ($parentNode->lft >= $parentNode->rgt) {
            throw new TreeInvalidLftRgtParent();
        }
        // Get a reference to the database
        $db = $this->getDbo();
        // Get the field names
        $fldRgt = $db->qn($this->getFieldAlias('rgt'));
        $fldLft = $db->qn($this->getFieldAlias('lft'));
        // Nullify the PK, so a new record will be created
        $this->{$this->idFieldName} = null;
        // Get the value of the parent node's rgt
        $myLeft = $parentNode->lft;
        // Update my lft/rgt values
        $this->lft = $myLeft + 1;
        $this->rgt = $myLeft + 2;
        // Update parent node's right (we added two elements in there, remember?)
        $parentNode->rgt += 2;
        // Wrap everything in a transaction
        $db->transactionStart();
        try {
            // Make a hole (2 queries)
            $query = $db->getQuery(true)->update($db->qn($this->tableName))->set($fldLft . ' = ' . $fldLft . '+2')->where($fldLft . ' > ' . $db->q($myLeft));
            $db->setQuery($query)->execute();
            $query = $db->getQuery(true)->update($db->qn($this->tableName))->set($fldRgt . ' = ' . $fldRgt . '+ 2')->where($fldRgt . '>' . $db->q($myLeft));
            $db->setQuery($query)->execute();
            // Insert the new node
            $this->save();
            // Commit the transaction
            $db->transactionCommit();
        } catch (\Exception $e) {
            // Roll back the transaction on error
            $db->transactionRollback();
            throw $e;
        }
        return $this;
    }