[{"_id":ObjectId("5a934e000102030405000000")},{"_id":ObjectId("5a934e000102030405000001")},{"_id":ObjectId("5a934e000102030405000002")}]

db.collection.find({_id:{"$in":[ObjectId("5a934e000102030405000000"),ObjectId("5a934e000102030405000001")]}})