Mongoose populate within an object?

Question

I'm not sure how to populate the sample schema below or if it is even possible. Can a reference be within an object like below? If you can, how would you populate it? E.g. .populate('map_data.location');?

var sampleSchema = new Schema({
  name: String,
  map_data: [{
    location: {type: Schema.Types.ObjectId, ref: 'location'},
    count: Number
  }]
});

Or will I have to have two separate arrays for location and count like so:

// Locations and counts should act as one object. They should
// Be synced together perfectly.  E.g. locations[i] correlates to counts[i]
locations: [{ type: Schema.Types.ObjectId, ref: 'location'}],
counts: [Number]

I feel like the first solution would be the best, but I'm not entirely sure how to get it working within Mongoose.

Thank you very much for any help!

Answer 1

The first solution is possible.

Mongoose currently has limitations (see this ticket here) populating multiple levels of embedded documents, however is very good at understanding nested paths within a single document - what you're after in this case.

Example syntax would be:

YourSchema.find().populate('map_data.location').exec(...)

Other features, such as specifying getters / setters on paths, orderBy and where clauses, etc. also accept a nested paths, like this example from the docs:

personSchema.virtual('name.full').get(function () {   return this.name.first + ' ' + this.name.last; }); 

Internally Mongoose splits the string at the dots and sorts everything out for you.

Answer 2

First option is ok, but if someone would have problems with that query map_data.location - Mongoose returns empty array instead of object - I found that this will work:

.populate({
     path: 'map_data.location',
     model: 'Location'
})

Answer 3

   YourSchema.find()
       .populate({
            path: 'map_data',
            populate: {
                path: 'location' 
            }
    }).exec(...)

The above statement will populate array of map_data and also the location object of each map_data.

hope this helps someone.