Mongoose Unique values in nested array of objects

Question

Mongoose Unique values in nested array of objects

For my project, I want to keep a mongoose document for groups of organizations, like this:

var groupSchema = Schema({
  name : { type : String },
  org : { type : Schema.Types.ObjectId, ref : 'Organization' },
  ...
  users : [{
    uid : { type : Schema.Types.ObjectId, ref : 'User' },
    ...
  }]
});

I want to prevent the same user from being in the same group twice. To do this, I need to force users.uid to be unique in the users array. I tried stating 'unique : true' for uid, but that didn't work. Is there a way to do this with mongoose or mongoDB without extra queries or splitting the schema?

Edit: I changed the previous value of uid to uid : { type : Schema.Types.ObjectId, ref : 'User', index: {unique: true, dropDups: true} } But this still doesn't seem to work.

Edit: Assuming there is no simple way to achieve this, I added an extra query checking if the user is already in the group. This seems to me the simplest way.

node.js
mongodb
mongoose

Answer 1

Use the $addToSet operator to add a value to an array only if the value is not already present.

Group.update({name: 'admin'}, {$addToSet: {users: userOid}}, ...

However, if the users array contains objects with multiple properties and you want to ensure uniqueness over just one of them (uid in this case), then you need to take another approach:

var user = { uid: userOid, ... };
Group.update(
    {name: 'admin', 'users.uid': {$ne: user.uid}}, 
    {$push: {users: user}},
    function(err, numAffected) { ... });

What that does is qualify the $push update to only occur if user.uid doesn't already exist in the uid field of any of the elements of users. So it mimics $addToSet behavior, but for just uid.