Knex Inserting Same Record Twice when Query Executed Asynchronously - node.js

Question

In my /api/v1/chats POST route I make an async call to user_chat_queries.addUserChat for each user_id passed in the request body. The idea is that if lots of user_id's come in I don't want to have each insertion await, instead I'd like to to dispatch all the insertions asynchronously so I do:
Asynchronous Route handler (https://github.com/caseysiebel/lang-exchange/blob/master/src/server/routes/chats.js#L57):
await Promise.all(user_ids.map((user_id) => {
return user_chat_queries.addUserChat(user_id, chat.id)
}));
As opposed to,
Synchronously:
for (let user_id of user_ids) {
await user_chat_queries.addUserChat(user_id, chat.id)
}
And in the user_chat_queries (https://github.com/caseysiebel/lang-exchange/blob/master/src/server/db/queries/user_chat.js#L5):
addUserChat: ( async (user_id, chat_id) => {
const user_chat = await userChats
.insert({ user_id, chat_id })
.returning('*')
const data = await db('user_chat').select('*')
return user_chat;
}),
Now the route is accessed from my test file: (https://github.com/caseysiebel/lang-exchange/blob/master/test/routes.chats.test.js#L83)
it('should add 2 user_chats', (done) => {
chai.request(server)
.post('/api/v1/chats')
.send({
created_at: Date.now(),
user_ids: [ 2, 4 ]
})
.end((err, res) => {
should.not.exist(err);
res.status.should.equal(201);
res.type.should.equal('application/json');
res.body.status.should.eql('success');
const chat = res.body.data;
chat.should.include.keys('id', 'created_at');
knex('user_chat')
.select('*')
.then((data) => console.log('data', data))
done();
});
});
The log shows that the { user_id: 4, chat_id: 3 } in inserted in the user_chat table twice.
The expected result (and the result when executed synchronously) is one { user_id: 2, chat_id: 3 } record and one { user_id: 4, chat_id: 3 } record are inserted into the user_chat table.
I can't track down what is causing this. It seems to me that addUserChat should insert a record made from the inputs it is passed each time, regardless of when it resolves.
Full code base: https://github.com/caseysiebel/lang-exchange
Debugging console output: https://gist.github.com/caseysiebel/262997efdd6467c72304ee783dadd9af#file-console-L5

Answer 1

you need to use mapSeries type mechanism (Which is not available on default Promise API). So, you may need to use other 3rd party library like bluebird.
more details bluebird mapSeries

Answer 2

You don't show what userChats is in your code examples, but it looks like you may have a global instance of knex that you reuse across different queries, such as:
const userChats = knex('user_chats')
This is not safe because each query building operation mutates the query builder. You may get away with it if you're running in series but when you run in parallel, both your addUserChat calls are using the same userChats query builder at the same time and weird stuff happens.
Rule of thumb: call knex() once for every query you build.