Send array as JSON response after the array is populated by values obtained from mongodb

Question

I am trying to send an array of document IDs as JSON response but the array I obtain as the response is empty. How can I make sure the array is populated first by the document IDs before it is sent as the response?

exports.createItem = async (req,res,next) => {
    let itemsIds = [];
    req.body.forEach( async element => {
        let doc = await Item.findOneAndUpdate({
            type: element.type,
            color: element.color,
            size: element.size
            }, {
            $inc:{stock: element.stock}
            }, {upsert:true, new: true});   
        itemsIds.push(doc._id);
        });
    res.status(200).json({
        success: true,
        itemsIds: itemsIds
    })
}

I want to make sure the res.status(200).json({...}) method runs only after all the doc ids are pushed to the mongo DB. Right now I just get the itemsIds as [ ] in the response. How I can make sure itemsIds array is populated by the doc ids first before sending the response?

Nayan Patel · Accepted Answer · 2019-08-14 12:48:34Z

2

The forEach loop contains a callback function, where we should not use async await, use the for of loop to await for the result, push it into the array and then send the response.

exports.createItem = async (req,res,next) => {
    let itemsIds = [];
    for (var element of req.body) {
        let doc = await Item.findOneAndUpdate({
            type: element.type,
            color: element.color,
            size: element.size
            }, {
            $inc:{stock: element.stock}
            }, {upsert:true, new: true});   
        itemsIds.push(doc._id);
    }
    res.status(200).json({
        success: true,
        itemsIds: itemsIds
    })
}

edited Aug 14, 2019 at 12:48

answered Aug 14, 2019 at 12:46

Nayan Patel

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3 Comments

Nayan Patel Over a year ago

@SagarChilukuri i have updated the answer, please find the answer.

JaxonFlexonWaxon Over a year ago

It works! Thank you. I will mark this answer as the best answer but can you please explain why this method works? Why does it work using for loop instead of forEach() ?

Nayan Patel Over a year ago

Once you give a function to forEach, it takes it as a asynchronous call, and its not handled by the main thread any more, so the main thread starts working on the next line, In your case it send the response.

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