使用带有Javascript的infiniteScroll过滤Firebase数据集

Question

I'm using Javascript (Ionic Framework) to load groups of Firebase sets (like Instagram), but I need to also filter the Firebase sets based on the value of the "sold" key in each data set. Here is one data set (there are many such sets):

The idea is if "sold" is false, then we load a given data set, if it's true, then we should not load it and skip it.

But there is a catch which makes this problem difficult. Please see the code next:

  doInfinite(infiniteScroll) {                                   
    if (this.end === false && (this.counter === 3 || this.counter === 8) && this.startListingID != undefined) {
      setTimeout(() => {                                                                              
        firebase.database().ref('/explore/').orderByKey().startAt((this.startListingID).toString()).limitToFirst(6).once('value', (snapshot) => {
          snapshot.forEach(snap => {         
            if((this.counter <= (this.counter2 + 4)) && (this.intermediateListingID !== snap.val().listingID) && this.end === false) {
              let temp = {
                Item: snap.val().Item,
                Price: snap.val().price,
                displayName: snap.val().displayName,
                sold: snap.val().sold,
                listingID: snap.val().listingID }
              this.object.push(temp);
              this.counter++;
              this.intermediateListingID = snap.val().listingID;
              return false;
            } else {
              if(this.startListingID !== snap.val().listingID) {
                this.counter = this.counter2;
                this.startListingID = snap.val().listingID;
              }
              else { this.end = true; }
            }
            setTimeout(() => {
              infiniteScroll.complete();
            }, 1000);
          });
          setTimeout(() => {
            infiniteScroll.complete();
          }, 1000);
        }).catch((error) => { console.log("infiniteScroll Error: " + JSON.stringify(error)); infiniteScroll.complete(); });
      }, 1000);
    } else {
      setTimeout(() => {
        infiniteScroll.complete();
      }, 1000);
    }
  }

I am just starting with coding, so I do realize the code above is rather bad, but it works.

The problem arises in cases where I would get "sold" data sets, and then the infinite scroll which is limitToFirst(6) turns to be less and the whole numbering logic screws up, not to mention if I get 6 sold data sets in a row, then nothing is shown and the scroll just breaks down.

If there a way (ideally on the level of Firebase) to FILTER all data sets with "sold = true" before they are fed into my infinite scroll logic?

Many thanks!

Answer 1

You could replace orderByKey with orderByChild('sold').equalTo(true)

firebase.database().ref('/explore/').orderByChild('sold').equalTo(true)
.limitToFirst(6).once('value', (snapshot) => {...

This should give you 6 items where sold = true . Unfortunately, you can't combine two filtering queries. So you'll either have to pull all the items and then just sort out which ones are sold after, or grab all the sold ones in random order. Though, if you're sorting by key this leads me to believe you don't need them sorted in any particular order, so you could go with this.