Express router not awaiting the forEach loop

Question

Express router is not awaiting my forEach loop and sends the old unmanipulated object as a response instead of the new manipulated data.

Here I am using Sequalize as my ORM.

router.get('/', async (req,res) => {
    try {
        let trainings = await db.Training.findAll();
        let locations = await db.Location.findAll();

        await locations.forEach(location => {
            trainings.forEach(training => {
                if(location.trainingId == training.id){
                    training["location"] = location
                }
            })
        })

        res.status(200).json({
            training:trainings
        })
    } catch(err) {
        console.log(err);
        res.status(404).json({
            message : err
        })
    }
})

Does this answer your question? [Using async/await with a forEach loop](https://stackoverflow.com/questions/37576685/using-async-await-with-a-foreach-loop) — Daniel_Knights, Jan 10 '21 at 15:21
I tried all the possible scenarios, it would be great if I get an answer with an example. That is if you can edit my code and show it to me it would be great. — madhan kumar, Jan 10 '21 at 15:24
Why are you awaiting that `forEach`? There's no Promise inside it — Daniel_Knights, Jan 10 '21 at 15:45
The issue must be due to something else. If you log `location.trainingId == training.id` what do you get? — Daniel_Knights, Jan 10 '21 at 15:56
`forEach` doesn't return a promise (it doesn't return anything!) so it can't be awaited. If you need to async work in sequence use a `for` or `for-of` loop. If you need to do async work in parallel, use `Promise.all`. — Dan Prince, Jan 10 '21 at 16:02
Everything works in console.log() but the response I get in postman is the origin unmanipulated object. — madhan kumar, Jan 10 '21 at 16:10
You need to catch all the promises and send the response after calling Promise.all(promises) — Jithin Zachariah, Jan 10 '21 at 16:44

score 0 · Answer 1 · answered Jan 10 '21 at 15:59

Basically you are using the await keyword against a synchronous process which is

locations.forEach(location => {
        trainings.forEach(training => {
            if(location.trainingId == training.id){
                training["location"] = location
            }
        })
    })

These lines of code doesn't return any promise or behave like a promise. So one solution can be having a function

function modify(trainings,locations){
    return new Promise((resolve,reject)=>{
        locations.forEach(location => {
        trainings.forEach(training => {
            if(location.trainingId == training.id){
                training["location"] = location
            }
        })
        })
        resolve('done')
    })
}

then have it like this

let trainings = await db.Training.findAll();
let locations = await db.Location.findAll();
await modify(trainings,locations)

or you can simply remove the await keyword from your current state of code.

This does not work, Everything works in console.log() but the response I get in postman is the origin unmanipulated object. — madhan kumar, Jan 10 '21 at 16:10

Express router not awaiting the forEach loop

1 Answers1