Wait for Getter in Mongoose to finish

Question

I currently have two collections: tours and groups. As a tour can have mutiple groups I would like to count all groups that have the id of a specific tour and provide this on my tour endpoint.

Group = require("../models/groupModel");

var tourSchema = mongoose.Schema({
    title: String,
    currentSize: {type: Number, get: getCurrentSize},
    ...
});

function getCurrentSize(currentSize) {
    var persons = 0;
    Group.find({ tour: this.id }, function (err, groups) {
      for (var i = 0; i < groups.length; i++) {
        persons += groups[i].persons;
      }
      return persons;
    });
}

However currentSize does not even get returned if I am using this getter. If I delete it, it will return a value stored in the document.

Is there any way to achieve this? I already tried it as a async function that leads to some "Query already executed" error.

Answer 1

Okay, I somehow got completely on the wrong track. After some good sleep I figured out that a virtual is what I need.

var tourSchema = mongoose.Schema({
    title: String,
    ...
});

tourSchema
  .virtual("currentSize", {
    ref: "group", // The model to use
    localField: "_id", // Find people where `localField`
    foreignField: "tour", // is equal to `foreignField`
  })
  .get(function (group) {
    var persons = 0;
    for (var i = 0; i < group.length; i++) {
      persons += parseInt(group[i].persons);
    }
    return persons;
  });

In my tourController.js I can then use something like this:

exports.index = async function (req, res) {
  const tours = await Tour.find({})
  .populate("currentSize")
  res.json(tours);
}