Mongoose .populated

index.js

const mongoose = require('mongoose');

mongoose.set('debug', true);

const GITHUB_ISSUE = `gh8247`;
const connectionString = `mongodb://localhost:27017/${ GITHUB_ISSUE }`;
const { Schema } = mongoose;

run().then(() => console.log('done')).catch(error => console.error(error.stack));

async function run() {
    await mongoose.connect(connectionString, { useNewUrlParser: true });
    await mongoose.connection.dropDatabase();

    const authorSchema = new Schema({
        name: { type: String, required: true },
    })

    const subSchema = new Schema({
        author: { type: Schema.Types.ObjectId, ref: 'Author', required: true },
        comment: { type: String, required: true },
    });

    const pageSchema = new Schema({
        title: { type: String, required: true },
        comments: { type: [subSchema], default: [], required: true },
    });

    const Author = mongoose.model('Author', authorSchema);
    const Page = mongoose.model('Page', pageSchema);

    const authorBob = await Author.create({ name: 'Bob Boberton' });
    const authorJane = await Author.create({ name: 'Jane Janerton' });

    const newPage = await Page.create({ title: 'This is a page' });
    newPage.comments.push({ author: authorBob, comment: 'Hello from Bob' });
    await newPage.save();

    const page = await Page.findOne().populate('comments.author');

    console.log(`Page comment authors populated("comments.author"): ${page.populated('comments.author')}`);
    console.log(page.comments[0].toObject());

    page.comments.push({ author: authorJane._id, comment: 'Hello from Jane' });

    console.log('--- Pushed in a comment from Jane ---');
    console.log(`Page comments length: ${page.comments.length}`);
    console.log('Page comment authors populated("comments.author"):', page.populated('comments.author'));
    page.comments.forEach((comment, index) => {
        console.log(`page.comments[${index}].populated('author') === ${page.comments[index].populated('author')}`);
    });

    await page.save();

    const pagePopulated = await Page.findOne().populate('comments.author');
    console.log(pagePopulated.populated('comments.author'));

    const pageUnpopulated = await Page.findOne();
    console.log(pageUnpopulated.populated('comments.author'));

    mongoose.connection.close();
}