Method _lock

/**
 * Method to lock the database table for writing.
 *
 * @return  boolean  True on success.
 *
 * @since   1.7.0
 * @throws  \RuntimeException
 */
protected function _lock()
{
    $this->_db->lockTable($this->_tbl);
    $this->_locked = true;
    return true;
}