Storing firestore objects in an array then sorting based on a numerical key

Question

Context

I've just queried all offers a specific user is eligible for, and have stored those objects in an array.
I'm now looking to sort them by priority (pri) so that I can place the first three on the user's dashboard
The sorting isn't happening, and I'm struggling to figure out why.

Code

    var offers = new Object;

    var offers = snap.data().offers;

    var offerpriority = new Array;

    offers.forEach(offer => {

        db.collection("offers").doc(offer).get().then(snap => {

            var thisoffer = {title: snap.data().title, pri: snap.data().priority};
            offerpriority.push(thisoffer);

        });

    });

    function compare(a, b){
        return b.pri-a.pri;
    };


    console.log(offerpriority.sort(compare));

Andrei Tigau · Accepted Answer · 2019-12-30 09:47:27Z

1

You should use the orderBy() method in order to sort items in Firestore.

You should use something like :

db.collection("offers").orderBy("pri");

Moreover, if you want to limit the results, like displaying 3 of them you can use the limit() method:

db.collection("offers").orderBy("pri").limit(3);

Here you can find a more detailed documentation regarding this discussion.

answered Dec 30, 2019 at 9:47

Andrei Tigau

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2 Comments

James Patrick Over a year ago

There's only a handful of offers that I want to get, the ones that appear in my user's offer array. Where would you think about adding that in?

Andrei Tigau Over a year ago

Probably for this you should iterate through the array and do a comparison query for each of the array element using the where('offers', '=', arrayElement) method. This solution is not so efficient, but I cannot think of anything else for the moment.

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