Method orderUp

/**
 * Method to move a node one position to the left in the same level.
 *
 * @param   integer  $pk  Primary key of the node to move.
 *
 * @return  boolean  True on success.
 *
 * @since   1.7.0
 * @throws  \RuntimeException on database error.
 */
public function orderUp($pk)
{
    $k = $this->_tbl_key;
    $pk = \is_null($pk) ? $this->{$k} : $pk;
    // Lock the table for writing.
    if (!$this->_lock()) {
        // Error message set in lock method.
        return false;
    }
    // Get the node by primary key.
    $node = $this->_getNode($pk);
    if (empty($node)) {
        // Error message set in getNode method.
        $this->_unlock();
        return false;
    }
    // Get the left sibling node.
    $sibling = $this->_getNode($node->lft - 1, 'right');
    if (empty($sibling)) {
        // Error message set in getNode method.
        $this->_unlock();
        return false;
    }
    try {
        // Get the primary keys of child nodes.
        $query = $this->_db->getQuery(true)->select($this->_tbl_key)->from($this->_tbl)->where('lft BETWEEN ' . (int) $node->lft . ' AND ' . (int) $node->rgt);
        $children = $this->_db->setQuery($query)->loadColumn();
        // Shift left and right values for the node and its children.
        $query->clear()->update($this->_tbl)->set('lft = lft - ' . (int) $sibling->width)->set('rgt = rgt - ' . (int) $sibling->width)->where('lft BETWEEN ' . (int) $node->lft . ' AND ' . (int) $node->rgt);
        $this->_db->setQuery($query)->execute();
        // Shift left and right values for the sibling and its children.
        $query->clear()->update($this->_tbl)->set('lft = lft + ' . (int) $node->width)->set('rgt = rgt + ' . (int) $node->width)->where('lft BETWEEN ' . (int) $sibling->lft . ' AND ' . (int) $sibling->rgt)->where($this->_tbl_key . ' NOT IN (' . implode(',', $children) . ')');
        $this->_db->setQuery($query)->execute();
    } catch (\RuntimeException $e) {
        $this->_unlock();
        throw $e;
    }
    // Unlock the table for writing.
    $this->_unlock();
    return true;
}