How to select certain fields with mongodb doctrine in symfony2
You will need to use QueryBuilder with the select operator:
$result = $dm->createQueryBuilder('User')->select('field1', 'field2')->field('field3')->equals('somevalue')->getQuery()->execute();
findBy does support operators, but the argument provided should be an array with the field name as key for the first dimension, like so :
$results = $yourRepositoryInstance->findBy(['somefield' => ['$in' => $arrayOfValues]]);
If you need to dynamically want to select fields, use the field name as an array.
$selects = ['field1','field2','field3']; // you can pass through api or else$result = $dm->createQueryBuilder('Collection')->select($selects)->getQuery()->execute();