/**
* Appends a locking clause to an SQL statement.
* This method *modifies* the +sql+ parameter.
*
* # SELECT * FROM suppliers FOR UPDATE
* add_lock! 'SELECT * FROM suppliers', :lock => true
* add_lock! 'SELECT * FROM suppliers', :lock => ' FOR UPDATE'
*
* @param string &$sql SQL statment.
* @param array $options TODO.
*/
public function addLock(&$sql, array $options = array())
{
$this->_write->addLock($sql, $options);
$this->_lastQuery = $this->_write->getLastQuery();
}