How to populate an array of model instances inside a subdocument? MongoDB Mongoose

Question

I have a subdocument that is nested as an array. Inside that subdocument I have references to other models. Using the .Find and .Populate methods I can receive the entire objects for single models referenced in the subdocument (check out Stop below) but not an array of model instances, Facts/Recommendations. For Facts/Recommendations I receive an array of object _ids . I can probably just take those _ids and make another query but this seems messy.

Is there a way to populate the array? Do I need to use Aggregate + $lookup? Is there a more Mongo way to restructure the Schema to simplify this?

Thank you for all and any help!

My subdocument called TourStop:

const mongoose = require('mongoose');

const Schema = mongoose.Schema;

const TourStopSchema = new Schema({
    stop: {
        type: Schema.Types.ObjectId,
        ref: 'Stop',
        required:[true, 'must have a Stop'],
    },
    mandatory: {
        type:Boolean,
        default: false
    },
    check_in_time: {
        type: Number,
        default: 0
    },
    order: {
        type:Number,
        required: [true, 'Must have an order']
    },
    facts: [{
        type: Schema.Types.ObjectId,
        ref: 'Fact'
    }],
    recommendations: [{
        type: Schema.Types.ObjectId,
        ref: 'Recommendation'
    }]
});


module.exports = TourStopSchema;

TourStops lives inside of Tour:

const mongoose = require('mongoose');
const TourStopSchema = require('../subdocs/tour_stop');
const Schema = mongoose.Schema;

const tourSchema = new Schema({
    name: {
        type:String,
        required:[true,'Name is required!'],
        unique: true
    },
    city: {
        type: String,
        required: [true, 'City is required!']
    },
    tourStops:[TourStopSchema]
});

const Tour = mongoose.model('Tour', tourSchema);
module.exports = Tour;

Stop Schema which is populated just fine.

const mongoose = require('mongoose');
const LocationSchema = require('../subdocs/location');
const ImageSchema = require('../subdocs/image');
const Schema = mongoose.Schema;

const stopSchema = new Schema({
    name:{
        type: String,
        required:[true,'Must have a name!']
    },
    location:LocationSchema,
    categories: {
        type: [String],
        default:[]
    },
    images:{
        type:[ImageSchema],
        default:[]
    }
});

const Stop = mongoose.model('Stop', stopSchema);
module.exports = Stop; 

And Fact Schema which is not populated correctly, instead returns an array of strings with the _ids

Fact:

const mongoose = require('mongoose');
const ImageSchema = require('../subdocs/image');
const Schema = mongoose.Schema;

const factSchema = new Schema({
    stop: {
        type: Schema.Types.ObjectId,
        ref:'Stop',
        required:[true, 'A Fact must have a Stop!'],
    },
    description: {
        type: String,
        required: [true,'A Fact must have a description!']
    },
    images: {
        type:[ImageSchema],
        default:[]
    }
});

const Fact = mongoose.model('Fact', factSchema);
module.exports = Fact;

And I'm running a test to check that the schema is properly hooked up to retrieve all the attributes of a TourStop:

it('saves a full relation graph', (done) => {
    User.findOne({ first_name: 'Dean' })
        .populate({
            // in that user find the tours property and load up all tours
            path: 'tours',
            // inside of all those tours, find the tourstops property and load all associated stops
            populate: {
                path: 'tour_stops.facts',
                model: 'Fact'
            },
            populate: {
                path: 'tour_stops.stop',
                model: 'Stop'
            }
        })
        // .populate('tours.tour_stops[0].facts')
        .then((user) => {
            // console.log(user.tours[0].tour_stops[0].stop);
            console.log(user.tours[0].tour_stops[0]);
            // console.log(Array.isArray(user.tours[0].tour_stops[0].facts))
            assert(user.first_name === 'Dean' );
            assert(user.tours.length === 1);
            assert(user.tours[0].name === "Awesome New Tour");
            assert(user.tours[0].tour_stops[0].stop.name === 'Jaffa Clock Tower');
            // assert(user.tours[0])
            // assert(user.blogPosts[0].title === 'JS is Great');
            // assert(user.blogPosts[0].comments[0].content === 'Congrats on great post!' );
            // assert(user.blogPosts[0].comments[0].user.name === 'Joe' )
            done();
        })
    })

Answer 1

You can use the following code to populate tours, stop, facts and recommendations. Note in model property, we should not give string value, but the model itself. So you need to import them to your code.

  User.findOne({ first_name: "Dean" })
    .populate({
      path: "tours",
      populate: {
        path: "tourStops.stop",
        model: Stop
      }
    })
    .populate({
      path: "tours",
      populate: {
        path: "tourStops.facts",
        model: Fact
      }
    })
    .populate({
      path: "tours",
      populate: {
        path: "tourStops.recommendations",
        model: Recommendation
      }
    })
    .then(user => {
       console.log(user);
    });