Sequelize get promise

Question

If I understand right I should be able to get the promise the way like that:

var helper = null;
MyModel.findAll().then(result => { helper = result });

In the examples this should be enough, but I do not get anything. If I assign a variable for the whole call I get promise pending. The only "difference" I see from the examples is that I call it in an http request:

exports.somePostRequest = (req, res, next) => {
var helper = null;
myModel.findAll().then(result => { helper = result });
}

This works perfectly:

exports.anOtherrequest = (req, res, next) => {
  myModel.findAll()
  .then(result => {
    res.status(200).json({message: result})})
}

Some of the examples I was looking at: https://sequelize.org/v3/docs/models-usage/ How to update a record using sequelize for node?

Any suggestion why this does not work?

Arpan Kc · Accepted Answer · 2021-10-03T13:58:36.420

1

var helper = null;
MyModel.findAll().then(result => { helper = result });
console.log(helper) // will be null

The problem with the approach above is that asynchronous operations like the one on line 2 will not happen in the order you expect it to. What happens in javascript is that line 1 executed, line 2 (asynchronous operation) is scheduled to run after all the synchronous operations gets executed, and line 3 runs, and finally all the asynchronous operations will complete (line 2 in this case).

So in simple words, the order of execution here is:

line 1 completes >> line 2 is scheduled to complete later >> line 3 completes >> line 2 operation completes

You can instead use await to make it go in order. Something like:

var helper = null;
helper = await MyModel.findAll();
console.log(helper); // not null; yayy

This way everything runs in order. But keep in mind, await operations should be inside an async function. So you're server should look something like:

exports.somePostRequest = async(req, res, next) => {
var helper = null;
helper = await myModel.findAll();
// or, var helper = await myModel.findAll();
// then do what you want with helper 
}

Alternative solution using .then

exports.somePostRequest = (req, res, next) => {
  myModel.findAll().then(result => 
    { 
       // work with the result here !
       // console.log(result);
    });
}

edited Oct 03 '21 at 13:58

answered Oct 03 '21 at 01:20

Arpan Kc

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I thought ".then" Meant to solve the async issue, or now? Also is not it bad to use async for http request? – Daniel Oct 03 '21 at 06:58
On an other thought; if this is the only way to essentially make it async and to be sync with awaits, then well. I just though there is an other solution for this – Daniel Oct 03 '21 at 08:56
1

`.then` does solve the async issue, but anything inside `.then` only runs once everything else has finished executing. So that means that any variable you assign inside `.then` will not be usable outside that scope. – Arpan Kc Oct 03 '21 at 12:11
1

In this case, if you need the helper variable to be used in the normal flow of execution, you will need to await for the result, or process the result inside the `.then`, there's no other way around it. – Arpan Kc Oct 03 '21 at 12:15
thank you, yes makes sense, I just reviewed .then, async await and everything is clear now! – Daniel Oct 03 '21 at 18:32

Sequelize get promise

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