Send single response after multiple updates - express

Question

I have an array of items that I am passing to an API endpoint (using Sequelize as my ORM). I'm trying to iterate over each item and update it, however I'm getting a Unhandled rejection Error: Can't set headers after they are sent.
stepsController.put = (req, res) => {
const { steps } = req.body;
// Steps is an array of objects that I want to update...
steps.map(step => {
Step.findOne({ where: { id: step.id } })
.then(savedStep =>
savedStep
.update({
order: step.order,
})
.then(success => res.status(200).send(success))
.catch(error => res.send(error))
)
.then(ok => res.status(200).send(ok))
.catch(err => res.send(err));
});
};
I believe this is because it's sending the response for each item. Sequelize's update method is a promise. How can I iterate over all of the items and make sure all of the items are updated before sending a single successful response?

Answer 1

There are three ways you can do
Promise.all
Co
Async Await
1) Here it is , you can use Promise.all :
stepsController.put = (req, res) => {
const { steps } = req.body;
// Steps is an array of objects that I want to update...
Promise.all(steps.map(step => {
return Step.findOne({ where: { id: step.id } }).then(savedStep =>
return savedStep.update({
order: step.order,
})
.catch(error => error)
).catch(err => err)
}))
.then(ok => res.status(200).send(ok))
.catch(err => res.send(err));
};
2) Another way is to use co :
const co = require('co');
stepsController.put = co.wrap(function* (req, res) => {
try {
const { steps } = req.body;
// Steps is an array of objects that I want to update...
for(let i=0;i<steps.length ; i++) {
let savedStep = yield Step.findOne({ where: { id: steps[i].id } });
if(savedStep)
yield savedStep.update({ order: steps[i].order});
}
res.status(200).send();
}
catch(err){
res.send(err);
}
});
3) If you’re using Node 8.0+ , there is no need of any package you can directly use async await :
stepsController.put = async(req, res) => {
try {
const { steps } = req.body;
// Steps is an array of objects that I want to update...
for(let i=0;i<steps.length ; i++) {
let savedStep = await Step.findOne({ where: { id: steps[i].id } });
if(savedStep)
await savedStep.update({ order: steps[i].order});
}
res.status(200).send();
}
catch(err){
res.send(err);
}
};