Get Knex.js transactions working with ES7 async/await

Question

I'm trying to couple ES7's async/await with knex.js transactions.

Although I can easily play around with non-transactional code, I'm struggling to get transactions working properly using the aforementioned async/await structure.

I'm using this module to simulate async/await

Here's what I currently have:

Non-transactional version:

works fine but is not transactional

app.js

// assume `db` is a knex instance

app.post("/user", async((req, res) => {
  const data = {
   idUser: 1,
   name: "FooBar"
  }

  try {
    const result = await(user.insert(db, data));
    res.json(result);
  } catch (err) {
    res.status(500).json(err);
  }
}));

user.js

insert: async (function(db, data) {
  // there's no need for this extra call but I'm including it
  // to see example of deeper call stacks if this is answered

  const idUser =  await(this.insertData(db, data));
  return {
    idUser: idUser
  }
}),

insertData: async(function(db, data) {
  // if any of the following 2 fails I should be rolling back

  const id = await(this.setId(db, idCustomer, data));
  const idCustomer = await(this.setData(db, id, data));

  return {
    idCustomer: idCustomer
  }
}),

// DB Functions (wrapped in Promises)

setId: function(db, data) {
  return new Promise(function (resolve, reject) {
    db.insert(data)
    .into("ids")
    .then((result) => resolve(result)
    .catch((err) => reject(err));
  });
},

setData: function(db, id, data) {
  data.id = id;

  return new Promise(function (resolve, reject) {
    db.insert(data)
    .into("customers")
    .then((result) => resolve(result)
    .catch((err) => reject(err));
  });
}

Attempt to make it transactional

user.js

// Start transaction from this call

insert: async (function(db, data) {
 const trx = await(knex.transaction());
 const idCustomer =  await(user.insertData(trx, data));

 return {
    idCustomer: idCustomer
  }
}),

it seems that await(knex.transaction()) returns this error:

[TypeError: container is not a function]

Answer 1

I couldn't find a solid answer for this anywhere (with rollbacks and commits) so here's my solution.

First you need to "Promisify" the knex.transaction function. There are libraries for this, but for a quick example I did this:

const promisify = (fn) => new Promise((resolve, reject) => fn(resolve));

This example creates a blog post and a comment, and rolls back both if there's an error with either.

const trx = await promisify(db.transaction);

try {
  const postId = await trx('blog_posts')
  .insert({ title, body })
  .returning('id'); // returns an array of ids

  const commentId = await trx('comments')
  .insert({ post_id: postId[0], message })
  .returning('id'); 

  await trx.commit();
} catch (e) {
  await trx.rollback();
}

Answer 2

Async/await is based around promises, so it looks like you'd just need to wrap all the knex methods to return "promise compatible" objects.

Here is a description on how you can convert arbitrary functions to work with promises, so they can work with async/await:

Trying to understand how promisification works with BlueBird

Essentially you want to do this:

var transaction = knex.transaction;
knex.transaction = function(callback){ return knex.transaction(callback); }

This is because "async/await requires the either a function with a single callback argument, or a promise", whereas knex.transaction looks like this:

function transaction(container, config) {
  return client.transaction(container, config);
}

Alternatively, you can create a new async function and use it like this:

async function transaction() {
  return new Promise(function(resolve, reject){
    knex.transaction(function(error, result){
      if (error) {
        reject(error);
      } else {
        resolve(result);
      }
    });
  });
}

// Start transaction from this call

insert: async (function(db, data) {
 const trx = await(transaction());
 const idCustomer =  await(person.insertData(trx, authUser, data));

 return {
    idCustomer: idCustomer
  }
})

This may be useful too: Knex Transaction with Promises

(Also note, I'm not familiar with knex's API, so not sure what the params are passed to knex.transaction, the above ones are just for example).

Answer 3

Here is a way to write transactions in async / await.

It is working fine for MySQL.

const trx = await db.transaction();
try {
    const catIds = await trx('catalogues').insert({name: 'Old Books'});
    const bookIds = await trx('books').insert({catId: catIds[0], title: 'Canterbury Tales' });
    await trx.commit();
} catch (error) {
    await trx.rollback(error);
}

Answer 4

For those who come in 2019.

After I updated Knex to version 0.16.5. sf77's answer doesn't work anymore due to the change in Knex's transaction function:

transaction(container, config) {
  const trx = this.client.transaction(container, config);
  trx.userParams = this.userParams;
  return trx;
}

Solution

Keep sf77's promisify function:

const promisify = (fn) => new Promise((resolve, reject) => fn(resolve));

Update trx

from

const trx = await promisify(db.transaction);

to

const trx =  await promisify(db.transaction.bind(db));