[{_id:ObjectId("5ab9cbe531c2ab715d42129a")},{_id:ObjectId("5ab9cbe531c2ab715d42129b")}]

db.collection.aggregate([{$match:{_id:{$nin:[ObjectId("5ab9cbe531c2ab715d42129a"),ObjectId("5ab9cbe531c2ab715d42129a")]}}}])