Method move

/**
 * Method to move a row in the ordering sequence of a group of rows defined by an SQL WHERE clause.
 *
 * Negative numbers move the row up in the sequence and positive numbers move it down.
 *
 * @param   integer  $delta  The direction and magnitude to move the row in the ordering sequence.
 * @param   string   $where  WHERE clause to use for limiting the selection of rows to compact the ordering values.
 *
 * @return  boolean  True on success.
 *
 * @since   1.7.0
 * @throws  \UnexpectedValueException
 */
public function move($delta, $where = '')
{
    // Check if there is an ordering field set
    if (!$this->hasField('ordering')) {
        throw new \UnexpectedValueException(sprintf('%s does not support ordering.', \get_class($this)));
    }
    $orderingField = $this->getColumnAlias('ordering');
    $quotedOrderingField = $this->_db->quoteName($orderingField);
    // If the change is none, do nothing.
    if (empty($delta)) {
        return true;
    }
    $row = null;
    $query = $this->_db->getQuery(true);
    // Select the primary key and ordering values from the table.
    $query->select(implode(',', $this->_tbl_keys) . ', ' . $quotedOrderingField)->from($this->_tbl);
    // If the movement delta is negative move the row up.
    if ($delta < 0) {
        $query->where($quotedOrderingField . ' < ' . (int) $this->{$orderingField})->order($quotedOrderingField . ' DESC');
    } elseif ($delta > 0) {
        $query->where($quotedOrderingField . ' > ' . (int) $this->{$orderingField})->order($quotedOrderingField . ' ASC');
    }
    // Add the custom WHERE clause if set.
    if ($where) {
        $query->where($where);
    }
    // Pre-processing by observers
    $event = AbstractEvent::create('onTableBeforeMove', ['subject' => $this, 'query' => $query, 'delta' => $delta, 'where' => $where]);
    $this->getDispatcher()->dispatch('onTableBeforeMove', $event);
    // Select the first row with the criteria.
    $query->setLimit(1);
    $this->_db->setQuery($query);
    $row = $this->_db->loadObject();
    // If a row is found, move the item.
    if (!empty($row)) {
        // Update the ordering field for this instance to the row's ordering value.
        $query->clear()->update($this->_tbl)->set($quotedOrderingField . ' = ' . (int) $row->{$orderingField});
        $this->appendPrimaryKeys($query);
        $this->_db->setQuery($query);
        $this->_db->execute();
        // Update the ordering field for the row to this instance's ordering value.
        $query->clear()->update($this->_tbl)->set($quotedOrderingField . ' = ' . (int) $this->{$orderingField});
        $this->appendPrimaryKeys($query, $row);
        $this->_db->setQuery($query);
        $this->_db->execute();
        // Update the instance value.
        $this->{$orderingField} = $row->{$orderingField};
    } else {
        // Update the ordering field for this instance.
        $query->clear()->update($this->_tbl)->set($quotedOrderingField . ' = ' . (int) $this->{$orderingField});
        $this->appendPrimaryKeys($query);
        $this->_db->setQuery($query);
        $this->_db->execute();
    }
    // Post-processing by observers
    $event = AbstractEvent::create('onTableAfterMove', ['subject' => $this, 'row' => $row, 'delta' => $delta, 'where' => $where]);
    $this->getDispatcher()->dispatch('onTableAfterMove', $event);
    return true;
}