Method _getNode

/**
 * Method to get nested set properties for a node in the tree.
 *
 * @param   integer  $id   Value to look up the node by.
 * @param   string   $key  An optional key to look up the node by (parent | left | right).
 *                         If omitted, the primary key of the table is used.
 *
 * @return  mixed    Boolean false on failure or node object on success.
 *
 * @since   1.7.0
 * @throws  \RuntimeException on database error.
 */
protected function _getNode($id, $key = null)
{
    // Determine which key to get the node base on.
    switch ($key) {
        case 'parent':
            $k = 'parent_id';
            break;
        case 'left':
            $k = 'lft';
            break;
        case 'right':
            $k = 'rgt';
            break;
        default:
            $k = $this->_tbl_key;
            break;
    }
    // Get the node data.
    $query = $this->_db->getQuery(true)->select($this->_tbl_key . ', parent_id, level, lft, rgt')->from($this->_tbl)->where($k . ' = ' . (int) $id);
    $query->setLimit(1);
    $row = $this->_db->setQuery($query)->loadObject();
    // Check for no $row returned
    if (empty($row)) {
        $e = new \UnexpectedValueException(sprintf('%s::_getNode(%d, %s) failed.', \get_class($this), $id, $k));
        $this->setError($e);
        return false;
    }
    // Do some simple calculations.
    $row->numChildren = (int) ($row->rgt - $row->lft - 1) / 2;
    $row->width = (int) $row->rgt - $row->lft + 1;
    return $row;
}