javascript - How to make unique identifier with 2 keys in mongoose? -

this question has answer here:

• mongoose: how define combination of fields unique? 2 answers

i don't know how explain question in title. sorry that.

here mean: have user model

var userschema = new schema({     username: { type: string, required: true },     messages: { type: number, required: true, default: 0 },     noticed: { type: date, required: true, default: date.now },     chatid: { type: number, required: true }     }) 

username , chatid may not unique, there should no users username , chatid both same!

meaning of there can not 2 users same username in 1 chat. user may in many different chats. how do in mongoose?

i think work:

userschema.index({ username : 1, chatid : 1 }, { unique : true });