db={"users":[{"_id":"1","name":"john","department":"IT"},{"_id":"2","name":"jane","department":"IT"},{"_id":"3","name":"bill","department":"finance"},{"_id":"4","name":"Bob","department":"IT"},{"_id":"5","name":"Mary","department":"IT"}],"meetings":[{"_id":"a","endedAt":100,"creator_id":"1","receiver_id":"2"},{"_id":"b","endedAt":150,"creator_id":"1","receiver_id":"3"},{"_id":"c","endedAt":200,"creator_id":"4","receiver_id":"2"},{"_id":"d","endedAt":250,"creator_id":"2","receiver_id":""}]}

db.users.aggregate([{"$match":{"department":{"$eq":"IT"}}},{"$lookup":{"from":"meetings","let":{"userid":"$_id"},"pipeline":[{"$match":{"$expr":{"$and":[{"$gt":["$endedAt",175]},{"$or":[{"$eq":["$$userid","$creator_id"]},{"$eq":["$$userid","$receiver_id"]}]}]}}},{"$project":{"_id":1}}],"as":"meetings"}},{"$match":{"$expr":{"$eq":["$meetings",[]]}}},{"$unset":["meetings"]}])