Array of ObjectIds will not populate without error

Question

I have the following mongoose schema:

var ChatSchema = new Schema({
    pin: String,
    users: [{type: mongoose.Schema.Types.ObjectId, ref: "User"}],
    messages: [{type: mongoose.Schema.Types.ObjectId, ref: 'Message'}], //<----
    active: Boolean,
});

var MessageSchema  = new Schema({
        sent: Date,
        user: {type: mongoose.Schema.Types.ObjectId, ref: 'User'},
        content: String
});

var UserSchema = new Schema({
    name: String,
    pin: String,
    id: String
});

This function is defined for the ChatSchema :

ChatSchema.methods.addMessageForUser = function(message, userid, userpin ) {
    chat = this;
        module.exports.User.findOne({id: userid, pin: userpin}).populate('messages').exec(function(err, user) {
             message = {
                user: user,
                time: new Date(),
                message: message,
            };
            chat.messages.push(message);
            chat.save();
        });

};

When I run it, I get the following error:

CastError: Cast to ObjectId failed for value "[object Object]" at path "messages"

If I remove populate('messages );` Then the error goes away, but I get another error because I try to use the messages array.

Here is the code for the models:

module.exports.Message = mongoose.model('Message', MessageSchema);

module.exports.User = mongoose.model('User', UserSchema);

module.exports.Chat = mongoose.model('Chat', ChatSchema);

Answer 1

Based on what you've got here, you're trying to populate backwards.

If each User had an array of Messages , then this populate call would work. It's a method on the mongoose Query object, in this case, and so it's looking for a property called messages on the documents in the User collection you're querying to pull ids from - since these aren't there, you get a weird error.

Based on what you've got here, it looks like it will work if you just remove the populate call.