Mongoose / Mongodb - should I explicitly add objectid to populate?

Question

So I have 2 models, one is users and the other is sessions.

It was initially setup as:

const users = mongoose.Schema({
    _id: mongoose.Schema.Types.ObjectId,
    username: {type: String, unique: true},
}
);
module.exports = mongoose.model('User', users,);

I then went on and added another model, called sessions,

const sessions = mongoose.Schema({
    _id: {type: mongoose.Schema.Types.ObjectId, default: mongoose.Schema.Types.ObjectId, null: false},
    user_id: {type: mongoose.Schema.Types.ObjectId, ref: 'User'},
    timestamp: {type: Date},
});

module.exports = mongoose.model('Sessions', sessions);

I then decided, I want to to be able to pull the user's sessions along with the users and added sessions: [{type: mongoose.Schema.Types.ObjectId, ref: 'SurfSessions', default: null}] to my users model schema.

I quickly learnt that users.findOne(username:admin).populate('sessions') isn't gonna fill up sessions by itself, as sessions returns as an empty array [].

Since I don't have sessions inside users populated with objectid's does that mean I cannot populate sessions or is there another way?

Please checkout [this](https://stackoverflow.com/questions/28179720/mongoose-populate-nested-array) post which has the similar question — Sivaraj P, Jun 07 '20 at 19:44
Thanks, been through that question many times before, but still doesn't answer my question. — Ronald Langeveld, Jun 07 '20 at 19:57

score 1 · Accepted Answer · answered Jun 08 '20 at 07:06

You should be able to do this with virtual populate:

const users = new mongoose.Schema(
  {
    _id: mongoose.Schema.Types.ObjectId,
    username: { type: String, unique: true },
  },
  { toJSON: { virtuals: true }, toObject: { virtuals: true } }
);
module.exports = mongoose.model('User', users);

Then:

userSchema.virtual('sessions', {
  ref: 'Session', // model to search in
  foreignField: 'user_id', 
  localField: '_id', // checks where user_id on session === _id on user
});

After this, use .populate('sessions') as normal. For more check this out: https://mongoosejs.com/docs/tutorials/virtuals.html#populate

Mongoose / Mongodb - should I explicitly add objectid to populate?

1 Answers1