Here is my query statement.
db.users.find({"_id":{"$in":[id0, id1, id2]}})
Of course it will return correct user array, but the sequence is random, it could be
[user1, user0, user2]
or
[user2, user0, user1]
it depends on ids' value.
If there is a way that I could force mongodb always return user array like this
db.users.find({"_id":{"$in":[id0, id1, id2]}}) => [user0, user1, user2]
db.users.find({"_id":{"$in":[id1, id0, id2]}}) => [user1, user0, user2]