Retrive custom object related photo

Hi, i have problems to retrive images related to some custom objects. I run this code:

Cloud.Objects.query({ classname : 'test', page : 1, per_page : 10, response_json_depth : 8,

    where : {
        id : Alloy.Globals.obj.id
    }
}

but the field photo_id does not appear in the list, i would like also to retrieve the photo object with the images utl inside. i test this param sel:{"all":["photo_id"]}, but does not work.

Someone can please help me? Thank you. Tommaso