Question

I’m working on a rating system. When a user rates, $inc increments the field, and addToSet adds the user_id to make sure the user only clicks rate once. I am checking if the user_id is already in the x field before updating, but that is another query which I’d rather avoid. Can I reach this purpose without having to write another query? I mean, $addToSet only adds if there is no value like that; can I instead get affected rows? Can you suggest other queries?

Thank you!

..->update(
    array("_id" => $idob),
    array(
       '$inc'      => array($type => (int) 1),
       '$addToSet' => array("x"   => (int) $user_id)
    )
);

Answer 1

Ok I see the problem.

..->update(
    array("_id" => $idob),
    array(
       '$inc'      => array($type => (int) 1),
       '$addToSet' => array("x"   => (int) $user_id)
    )
);

The problem is that you need a conditional $inc there so that it only $incs if it does add to set.

This is not possible with a unique index since unique indexes work from the root of the document atm. Also you probably want to use the $inc as a form of pre-aggregation or what not.

One method could be:

update(
    array('_id' => $idob, 'x' => array('$nin' => array($user_id))), 
    array(
        '$inc' => array($type => 1),
        '$push' => array('x' => (int)$user_id)
    )
)

This will only do the update if that user_id does not already exist in x.