Handling async operation in mongoose virtual property

I created a virtual property on the users schema called debt

the debt property is to return the sum aggregate of each user total debt from the Bill model

But the virtual field debt keeps returning Promise { <pending> }

Here is my code sample:

userSchema.virtual('debt').get(async function () {
    const bills = await this.model('Bill').aggregate([
        {
            $match: {
                $and: [{ 'user._id': this._id }, { balance: { $gt: 0 } }]
            }
        },
        {
            $group: { _id: null, total: { $sum: "$balance" } }
        }
    ]);
    console.log(bills) // [{_id: null, total: theSummedValue }]
    return bills[0].total; // Promise { <pending> }
});

how can I return theSummedValue ??

See issue#1894 and issue#5762

> virtuals are just getters/setters, which are assumed to be synchronous

You can add a custom instance method instead.

E.g.("mongoose": "^7.2.1")

import mongoose from 'mongoose';
import { config } from '../../config';

mongoose.set('debug', true);

const userSchema = new mongoose.Schema({
	name: String,
});
userSchema.method('dept', async function () {
	console.log(this);
	// @ts-ignore
	const result = await mongoose.model('bill').aggregate([
		{
			$match: {
				$and: [{ 'user._id': this._id }, { balance: { $gt: 0 } }],
			},
		},
		{
			$group: { _id: null, total: { $sum: '$balance' } },
		},
	]);
	return result[0].total;
});
const User = mongoose.model('user', userSchema);

const billSchema = new mongoose.Schema({
	balance: Number,
	user: userSchema,
});
const Bill = mongoose.model('bill', billSchema);

(async function main() {
	try {
		await mongoose.connect(config.MONGODB_URI);
		await Promise.all([User, Bill].map((m) => m.collection.drop()));
		// seed
		const [user1, user2] = await User.create([{ name: 'Nick' }, { name: 'Jack' }]);
		await Bill.create([
			{ balance: 100, user: user1 },
			{ balance: 200, user: user1 },
			{ balance: 0, user: user1 },
			{ balance: 50, user: user2 },
		]);
		//@ts-ignore
		const dept = await user1.dept();
		console.log("Nick's dept: ", dept);
	} catch (error) {
		console.error(error);
	} finally {
		await mongoose.connection.close();
	}
})();

Output:

Mongoose: users.drop()
Mongoose: bills.drop()
Mongoose: users.insertOne({ name: 'Nick', _id: ObjectId("6498f33d24d77a71b4976083"), __v: 0 }, {})
Mongoose: users.insertOne({ name: 'Jack', _id: ObjectId("6498f33d24d77a71b4976084"), __v: 0 }, {})
Mongoose: bills.insertOne({ balance: 100, user: { name: 'Nick', _id: ObjectId("6498f33d24d77a71b4976083"), __v: 0 }, _id: ObjectId("6498f33d24d77a71b4976087"), __v: 0}, {})
Mongoose: bills.insertOne({ balance: 200, user: { name: 'Nick', _id: ObjectId("6498f33d24d77a71b4976083"), __v: 0 }, _id: ObjectId("6498f33d24d77a71b4976089"), __v: 0}, {})
Mongoose: bills.insertOne({ balance: 0, user: { name: 'Nick', _id: ObjectId("6498f33d24d77a71b4976083"), __v: 0 }, _id: ObjectId("6498f33d24d77a71b497608b"), __v: 0}, {})
Mongoose: bills.insertOne({ balance: 50, user: { name: 'Jack', _id: ObjectId("6498f33d24d77a71b4976084"), __v: 0 }, _id: ObjectId("6498f33d24d77a71b497608d"), __v: 0}, {})
{ name: 'Nick', _id: new ObjectId("6498f33d24d77a71b4976083"), __v: 0 }
Mongoose: bills.aggregate([ { '$match': { '$and': [ { 'user._id': new ObjectId("6498f33d24d77a71b4976083") }, { balance: { '$gt': 0 } } ] } }, { '$group': { _id: null, total: { '$sum': '$balance' } } }], {})
Nick's dept:  300