Doctrine call MongoCursor::rewind when I try get singleResult from Query

[vsychov]

Hi, I found some strange issue, when I try to get single record from DB, by code:

$this
    ->createQueryBuilder()
    ->field('field1')->equals('value1')
    ->getQuery()
    ->getSingleResult();

then Cursor::toArray, convert cursor to array by iterator_to_array, and iterator_to_array call MongoCursor::rewind (it's not good for perfomance).

If I call findOneBy, MongoCursor::rewind not called.

[jmikola]

Do you have evidence that the query is actually being executed multiple times? Or is the concern just that we're invoking a couple of extra cursor methods (through iterator_to_array()'s execution)?

Cursor::getSingleResult() does reset the cursor before and after executing it, but rewind() should only be called once. The iterator_to_array() behavior should be no different than iterating with foreach and breaking after the first iteration, since we're limiting the reset set to one document.

At the driver level, MongoCursor::findOne() is effectively doing the same thing as MongoCursor::rewind(), followed by valid() and current(). iterator_to_array() effectively calls those methods for us.

Doctrine MongoDB's query builder works against a cursor, which allows it work nicely with the cursor provided for ODM (when hydration is required). For that reason, we don't have a code path that shortcuts to MongoCollection::findOne().