Node.js 7 how to use sequelize transaction with async / await?

Question

Node.js 7 and up already support async/await syntax. How should I use async/await with sequelize transactions?

Answer 1

If CLS is enabled, Sequelize can use that to keep your transaction object and automatically pass it to all queries inside the continuation-passing cycle.

Setup:

import { Sequelize } from "sequelize";
import { createNamespace } from "cls-hooked"; // npm i cls-hooked

const cls = createNamespace("transaction-namespace"); // any string
Sequelize.useCLS(cls);

const sequelize = new Sequelize(...);

Usage:

const removeUser = async (id) => {
    await sequelize.transaction(async () => { // no need `async (tx)`
        await removeClasses(id);
        await User.destroy({ where: { id } }); // will auto receive `tx`
    });
}

const removeClasses = async (userId) => {
    await UserClass.destroy({ where: { userId } }); // also receive the same transaction object as this function was called inside `sequelize.transaction()`
    await somethingElse(); // all queries inside this function also receive `tx`
}

How it works?

From Sequelize source code: github.com/sequelize

Check and save transaction to CLS

if (useCLS && this.sequelize.constructor._cls) {
    this.sequelize.constructor._cls.set('transaction', this);
}

Retrieve transaction from CSL and set to options

if (options.transaction === undefined && Sequelize._cls) {
    options.transaction = Sequelize._cls.get('transaction');
}

Read more:

1. Sequelize: automatically pass transactions to all queries
2. CLS hooked
3. Async Hooks