db={local:[{_id:1},{_id:2},{_id:3}],metrics:[{_id:4,ownerIds:[1,2]},{_id:5,ownerIds:[3]}]}

db.local.aggregate([{"$lookup":{"from":"metrics","as":"metrics",localField:"_id",foreignField:"ownerIds","pipeline":[{"$project":{"fieldName":1,"ownerIds":1,"auth0Cache":1}}],}}])