Mongoose 6: Populate not working on array field with defined subdocument schema

[skrishnan22]

These are my schemas

user.js

const mongoose = require("mongoose");

const schema = new mongoose.Schema(
  {
    firstName: String,
    companies: {
      type: [
        {
          companyId: {
            type: mongoose.Schema.Types.ObjectId,
          },
          companyName: String,
        },
      ],
      required: true,
    },
  },
  {
    toObject: {
      virtuals: true,
    },
  }
);


schema.virtual("companies.details", {
  ref: "company",
  localField: "companies.companyId",
  foreignField: "_id",
  justOne: true,
});

schema.set("collection", "users");

module.exports = mongoose.model("user", schema);

company.js

const mongoose = require("mongoose");

const schema = new mongoose.Schema({
  name: {
    type: String,
  },
  legalName: {
    type: String,
    required: true,
  },
});

schema.set("collection", "companies");

module.exports = mongoose.model("company", schema);

On running

User.findOne({firstName:'ABC'}).populate('companies.details');

in mongoose 5, companies.details is being populated correctly, but in mongoose 6 the populate is not happening

The populate works in mongoose 6, if I change the User schema as below. Note the change to companies field

const mongoose = require("mongoose");

const schema = new mongoose.Schema(
  {
    firstName: String,
    email: String,
    companies: {
      type: [{}],
      required: true,
    },
  },
  {
    toObject: {
      virtuals: true,
    },
  }
);

schema.virtual("companies.details", {
  ref: "company",
  localField: "companies.companyId",
  foreignField: "_id",
  justOne: true,
});

schema.set("collection", "users");

module.exports = mongoose.model("user", schema);

Is this expected change when migrating from 5 to 6 and if so what is the best way to make it work with versions 6 and above

[skrishnan22]

On further debugging, noticed this

1. With debug true, could observe the db query for fetching companies for populating is being executed in mongoose 6 as well.
2. The populated details virtual is part of $$populatedVirtuals of companies EmbeddedDocument in version 6 as against part of _doc object in version 5.

[vkarpov15]

@skrishnan22 what is the exact version of Mongoose you're using? The following script works as expected for me on v6.10.4. Can you please confirm whether the following script works for you?

const mongoose = require('mongoose');

const userSchema = new mongoose.Schema(
  {
    firstName: String,
    companies: {
      type: [
        {
          companyId: {
            type: mongoose.Schema.Types.ObjectId,
          },
          companyName: String,
        },
      ],
      required: true,
    },
  },
  {
    toObject: {
      virtuals: true,
    },
    toJSON: { virtuals: true }
  }
);

userSchema.virtual("companies.details", {
  ref: "company",
  localField: "companies.companyId",
  foreignField: "_id",
  justOne: true,
});

userSchema.set("collection", "users");

const Company = mongoose.model("company", companySchema);

async function run() {
  await mongoose.connect('mongodb://localhost:27017');
  await mongoose.connection.dropDatabase();

  const company = await Company.create({
    name: 'Google',
    legalName: 'Alphabet Inc'
  });
  const user = await User.create({
    firstName: 'Test',
    companies: [{ companyId: company._id, companyName: 'Google' }]
  });

  const test = await User.findOne().populate('companies.details');
  console.log(
    'what is test',
    test.toObject({ virtuals: true }), // includes 'details'
    test.companies[0].details // includes 'legalName: "Alphabet Inc"'
  );
}

run();