Node API - res.send() from 2nd loop

Question

I'm trying to return the hole master/detail object to client, but detail is coming as an empty array Like this post I've also ended with the same problem:

"Can't call res.send(data) inside the loop because res.send() can only be called once." "But if I call res.send(array) outside of the loop, the array is still empty"

What is the right way to do it? I'm trying not to use use asyn

    var getMasterDetail = function (req, res) {

        const key = "Detail";
        var list = {}
        list[key] = []
        var modelsMaster = objModels.ObjMaster
        var modelsDetail = objModels.objDetail
         modelsMaster.getMasters(objModels.hdb, (e, master) => {
            if (e) {
                return console.log(e);
            }              

            for (i = 0; i < master.length; i++) {
                modelsDetail.getDetails(objModels.hdb, master[i].nrMaster, (e, detail) => {
                    if (e) {
                        return console.log(e);
                    }

                    for (j = 0; j < detail.length; j++) {

                        list[key].push(detail[j])
                    }

                })
                master[i].DetailList = list           
            };

            res.send({ MasterDetail: master })

        })

    };

Thanks.

UPDATE: The answer from @Hammerbot was almost right, but, I have not notice at the time, that I was getting the same detail for all masters. Ex. {master:{1,2,3,4,5,6}, master{1,2,3,4,5,6}} instead of {master:{1,2,3}, master{4,5,6}}

I Have no any idea why and how to fix it. I've tried to clean the list befor the loop, and move master master[i].DetailList, creating a second Promisse for the second loop, no success.

If you're using callbacks, using the async.forEach is probably the right way to go. Your code will probably be a lot simpler if use promises though. — schu34
– schu34, Commented Nov 16, 2018 at 15:26
Seconding @schu34's recommendation of Promises. Promise.all seems like an excellent fit here. — Connor
– Connor, Commented Nov 16, 2018 at 15:27

Hammerbot · Accepted Answer · 2018-11-16 15:31:36Z

1

You should use promises for that. Here is an example that should resolve your problem:

var getMasterDetail = function (req, res) {

    const key = "Detail";
    var list = {}
    list[key] = []
    var modelsMaster = objModels.ObjMaster
    var modelsDetail = objModels.objDetail
    modelsMaster.getMasters(objModels.hdb, (e, master) => {
        if (e) {
            return console.log(e);
        }

        const promises = []

        for (i = 0; i < master.length; i++) {
            const promise = new Promise(resolve => {
                master[i].DetailList = list
                modelsDetail.getDetails(objModels.hdb, master[i].nrMaster, (e, detail) => {
                    if (e) {
                        return console.log(e);
                    }

                    for (j = 0; j < detail.length; j++) {
                        list[key].push(detail[j])
                    }
                    resolve()
                })
            })

            promises.push(promise)
        }

        Promise.all(promises).then(() => {
            res.send({ MasterDetail: master })
        })
    })

};

As you can see, before the loop I initiate a promises array. Inside the loop, I create a promise by iteration that gets resolved when the callback has finished.

I push the promise into the promises Array, and at the end I use Promise.all() to wait for all the promises to get resolved before sending the result in the response.

answered Nov 16, 2018 at 15:31

Hammerbot

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2 Comments

Marisco Over a year ago

Thank you very much Sr. @Hammerbot, worked like a charm!

Marisco Over a year ago

I have not notice at the time, but now I'm getting the same detail for all masters, any idea why and how to fix it? I've tried to clean the list and move master master[i].DetailList = list no sucess.

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