Mongoose populate multiple nested documents

Question

I've searched high and low but can't figure out how to form the following populate query, first here are my models:

const CourseSchema = new Schema({
    classes: [{ type: Schema.Types.ObjectId, ref: 'Classroom' }]
});

const ClassSchema = new Schema({
    location: { type: mongoose.Schema.Types.ObjectId, ref: 'Location' },
    instructors: [{ type: mongoose.Schema.Types.ObjectId, ref: 'User' }],
});

I have an endpoint which gets a single course, but I want to populate the classes field AND the location and instructors fields in classes. Right now, I can either populate the instructors field in classes or location, but I can't populate both of them at the same time. This is what I have for now:

    Course
        .findById(req.params.courseId)
        .populate({
            path: 'classes',
            populate: {
                path: 'instructors',
                model: 'User'
            }
        })

How can I also populate the location field in classes?

Thanks.

Answer 1

An interest alternative is pass an array to nested populate.

Course
    .findById(req.params.courseId)
    .populate({
        path: 'classes',
        model: 'Classroom',
        populate: [{
            path: 'instructors',
            model: 'User'
        },
        {
            path: 'location',
            model: 'Location'
        }]
    })

Answer 2

Try the below code    


getAllByQuery: function (query, callback) {
    this
      .find(query, {capId: 1})
      .populate({path: 'capId',
        model: 'cap',
        select: {
          'capDetail': 0,
          'area': 0,
        },
        populate: [{
          path: 'ad_Id',
          model: 'Ad',
          select: { 'Level': 1}
        },
        {
          path: 'ctgs',
          model: 'Ctgry',
          select: { '_id': 0}
        }]
      })
      .exec(callback);
  }