db={"item":[{"_id":1,"item":"almonds","price":12,"quantity":2},{"_id":2,"item":"pecans","price":20,"quantity":1},{"_id":3,"item":"orange","price":20,"quantity":1},{"_id":4,"item":"apple","price":20,"quantity":1}],"item_recovery":[{"_id":1,"item":"almonds","price":12,"quantity":2},{"_id":2,"item":"pecans","price":20,"quantity":1},{"_id":3,"item":"orange","price":20,"quantity":1}]}

db.item.aggregate([{"$lookup":{"from":"item_recovery","localField":"_id","foreignField":"_id","pipeline":[{"$project":{_id:1}}],"as":"hasRecovery"}},{$match:{$expr:{$eq:[{$size:"$hasRecovery"},0]}}},{$unset:"hasRecovery"}])