php - cakephp save update data from old data value + new value -

I do not know the keyword to search with my problem How to save the update data in a field that already A value exists and I want to update it with additional value.

Here is an example cakephp:

  $ userData = array ('id' = & gt; $ userId, 'credit' => $ newCredit // Only updates new credits); $ This- & gt; User- & gt; Save ($ userdata);  

If I use the usual query MySQL, then it will be like this:

  mysql_query ("UPDATE` user` set` credit` = `credit `+ '$ NewCredit' where` id` = '$ userId' ");  

You can see only one time to update the normal code with the existing code credit I know that I SELECT I can do this data using and can operate in php , then return the UPDATE data, but it will be 2 times (select, then update).

So what can cakephp do it at once? And how: D?

will work

  $ this-> gt; ; User- & gt; Updates (Array ('credit' = & gt; "Credit + $ new credit)", array ('id' => user $ Id););