MongoDB, NodeJS. Get element from promise

Question

I have request to DB with promises, I want to extract 2 values("latitude" and "longitude") for all documents and put it to array.

I'm doing like this;

const promises = [
    dbo.collection("users").find({ name: "Mark" }, { latitude: 1, longitude: 1, _id: 0 }).toArray()
]
Promise.all(promises).then(function (Presults) {
        console.log(Presults);


    }).catch(function (err) {
        console.log(err);
    });

as a result I get all fields, for example: name, gender, latitude, longitude etc. When I try to specify that I want only latitude, longitude, I always get result undefined What I've tried: console.log(Presults.latitude); console.log(Presults[0].latitude);

But I want get output array like this

[
    { lat: -31.563910, lng: 147.154312 },
    { lat: -33.718234, lng: 150.363181 },
    { lat: -33.727111, lng: 150.371124 },
    { lat: -33.848588, lng: 151.209834 }
];

I tested without promises, it works:

    dbo.collection("users").find(
    { name: "Mark" },
    { latitude: 1, longitude: 1, _id: 0 }).toArray(function (err, result) {
        if (err) throw err;
        var array1 = [];
        var z = { "lat": result[0].latitude, "lng": result[0].longitude };
        var y = { "lat": result[0].latitude, "lng": result[0].longitude };
        array1.push(z, y);

        console.log(array1);
    });

can you show what exactly you get when you console.log(Presults); this — Shijil Narayanan
– Shijil Narayanan, Commented May 30, 2020 at 13:09
Could you add what exacly you got with console.log(Presults);? — Sa1m0n
– Sa1m0n, Commented May 30, 2020 at 13:10
try replacing {latitude: 1, longitude: 1, _id: 0} with '+latitude +longitude -_id'... — bloo
– bloo, Commented May 30, 2020 at 13:10
This is what I get: [ [ { _id: 'fiougisudfgy890-milmb:AP897rjhkgs9SooLQSqgXQqfPmHbIV166kL7ojR4n456734523AuOTv6KSbQZiLZZerty456jz7VwlqzQN', name: 'Mark', token: 'fPKrkfirog38960-milmb:APA91bGeK3OavT704978iofghbQZiLZZOHb6pLP39836ghqzQN', email: '[email protected]', Aid: '860a8ggirpww4565b2d', OS: '9', latitude: 26.521511, longitude: 52.1424 } ] ] — Andrei Charnyshou
– Andrei Charnyshou, Commented May 30, 2020 at 13:17
Ashwyn, this is not changing anything. It is just for search. My problem is with extraction data from result — Andrei Charnyshou
– Andrei Charnyshou, Commented May 30, 2020 at 13:20

Shijil Narayanan · Accepted Answer · 2020-05-30 13:59:02Z

1

Try this

Promise.all(promises).then(function (results) {
    const data = results.flatMap(v => v.map(k => ({ lat: k.latitude, lng: k.longitude})))

    console.log(data)
})

edited May 30, 2020 at 13:59

answered May 30, 2020 at 13:21

Shijil Narayanan

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7 Comments

Andrei Charnyshou Over a year ago

it is not changing anything, it still returns full list of elements. I need to output only two parameters: latitude and longitude.

Shijil Narayanan Over a year ago

I have updated the answer, u need to remove toArray() from the promise first

Andrei Charnyshou Over a year ago

output of your code is: [ { lat: undefined, lng: undefined } ] btw, valued in DB in double. I tried with toArray() and without - result is the same

Shijil Narayanan Over a year ago

can u show what comes when you do a console.log(results)

Andrei Charnyshou Over a year ago

it is too big to post as a comment, it is smth like this [ Cursor { _readableState: ReadableState { objectMode: true, highWaterMark: 16,

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