[Typo3-dev] Howto safely increase DB value

[Kraft Bernhard]

Hallo list,


In a site I have a selfmade FE-Plugin which needs to increase the value of a DB-field (int)
whenever the user clicks a link.

With simple SQL I would do it like:
UPDATE mytable SET field=field+1 WHERE uid=123;

This ensures that if two instances of the programm execute the same SQL query at almost the
same time that the value gets increases 2 times.

However if i do:
$res = $GLOBALS['TYPO3_DB']->exec_SELECTquery('field', 'mytable', 'uid=123');
$row = $GLOBALS['TYPO3_DB']->sql_fetch_assoc($res);
$GLOBALS['TYPO3_DB']->exec_UPDATEquery('mytable', 'uid=123', array('field' => (intval($row['field'])+1)));

it is not safe that not at some time two script run, each one fetches the actual value
and then each script sets the resulting value to just one more than before ...


How to cope with this ?

The exec_UPDATEquery function can't get used for this ?

Will I have to use the "mysql" method and break DBAL compatibility (it is not needed for this site
as it will never run with another DB than mysql ... but I'm already somehow used to the DBAL API calls)


greets,
Bernhard
-- 
Kraft Bernhard
MOKKA Medienagentur <http://www.mokka.at>
T: +43 - 1 - 895 33 33 - 50