how to get recursively all objects attached to a model in mongoose

imagine these two nested mongoose models, a Vote containing a list of Candidates

    var candidateSchema = new Schema({
        name: String
    });

    var voteSchema = new Schema({
        candidates: [{ type: Schema.Types.ObjectId, ref: 'Candidate' }]
    });

    voteSchema.methods.addCandidate = function addCandidate(newCandidate, callback) {
        this.candidates.addToSet(newCandidate);
        this.save(callback);
    };

    var Vote = mongoose.model('Vote', voteSchema);
    var vote = new Vote();

    var Candidate = mongoose.model('Candidate', candidateSchema);
    var candidate = new Candidate({ name: 'Guillaume Vincent' });
    vote.addCandidate(candidate);

    console.log(vote); // { _id: 53d613fdadfd08d9ebea6f88, candidates: [ 53d68476fc78cb55f5d91c17] }
    console.log(vote.toJSON()); // { _id: 53d613fdadfd08d9ebea6f88, candidates: [ 53d68476fc78cb55f5d91c17] }

If I use candidates: [candidateSchema] instead of candidates: [{ type: Schema.Types.ObjectId, ref: 'Candidate' }] then console.log(vote); display :

{
    _id: 53d613fdadfd08d9ebea6f88, 
    candidates: [ { _id: 53d613fdadfd08d9ebea6f86, name: 'Guillaume Vincent' } ] 
}

My question is :

With candidates: [{ type: Schema.Types.ObjectId, ref: 'Candidate' }] how can I get recursively all objects attached to a model ? same behavior with candidates: [candidateSchema]

I'm not using embedded schema because I want my Vote to be updated when I update my Candidate (see http://stackoverflow.com/a/14418739/866886)