[{_id:1,objects:[{prop_1:"...",foo:true},{prop_1:"...",foo:false},{prop_1:"..."}]},{_id:2,objects:[{prop_1:"...",foo:false},{prop_1:"...",foo:false},{prop_1:"..."}]},{_id:3,objects:[{prop_1:"...",foo:true},{prop_1:"...",foo:true},{prop_1:"...",foo:true}]}]

db.collection.find({$expr:{$allElementsTrue:"$objects.foo"}})