Firestore + AngularFire2 分页(按范围查询项目 - .startAfter(lastVisible) ) [英] Firestore + AngularFire2 pagination ( query items by range - .startAfter(lastVisible) )

问题描述

在一个组件中，我想从 FireStore 中提取一系列项目，例如.从 0 到 5，从 5 到 10 等等.我找到了 this 在 FireStore 的文档中，但他们不使用 AngularFire2，所以我越努力尝试重构，因为我得到了更大的混乱.我通过简单的 splice()'ing 使它工作:

In a component I want to pull a range of items from FireStore, for ex. from 0 to 5, from 5 to 10 etc. I found this in FireStore's docs, but they dont use AngularFire2 so as harder I tried to refactor as bigger mess I got. I made it working by simply splice()'ing:

service ->

topFirstScores(): AngularFirestoreCollection<Score> {
  return this.fireRef.collection('scores', r => r
          .orderBy('score', 'desc').limit(6)
  );
}

component ->

$scores = new Subject();

this.scores$ = this.$scores.asObservable();
if (this.scores === 'first') {
  this.scoreS.topFirstScores().valueChanges().take(1)
    .subscribe(_ => this.$scores.next(_.splice(0, 3)))
} else {
  this.scoreS.topFirstScores().valueChanges().take(1)
    .subscribe(_ => this.$scores.next(_.splice(3, 3)))
}

但这似乎更像是一种解决方法.谁能翻译一下:

But this seems more as a workaround. Could anyone translate this:

var first = db.collection("cities")
        .orderBy("population")
        .limit(25);

return first.get().then(function (documentSnapshots) {
  // Get the last visible document
  var lastVisible = documentSnapshots.docs[documentSnapshots.docs.length-1];
  console.log("last", lastVisible);

  // Construct a new query starting at this document,
  // get the next 25 cities.
  var next = db.collection("cities")
          .orderBy("population")
          .startAfter(lastVisible)
          .limit(25);
});

最好返回 AngularFirestoreCollection?

推荐答案

我遇到了同样的问题，这就是我所做的.

I had the same Problem and this is what i did.

private _data: BehaviorSubject<Scores[]>;
public data: Observable<Scores[]>;
latestEntry: any;

constructor(private afs: AngularFirestore) {}

// You need to return the doc to get the current cursor.
  getCollection(ref, queryFn?): Observable<any[]> {
    return this.afs.collection(ref, queryFn).snapshotChanges().map(actions => {
      return actions.map(a => {
        const data = a.payload.doc.data();
        const id = a.payload.doc.id;
        const doc = a.payload.doc;
        return { id, ...data, doc };
      });
    });
  }
// In your first query you subscribe to the collection and save the latest entry
 first() {
  this._data = new BehaviorSubject([]);
  this.data = this._data.asObservable();

  const scoresRef = this.getCollection('scores', ref => ref
    .orderBy('score', 'desc')
    .limit(6))
    .subscribe(data => {
      this.latestEntry = data[data.length - 1].doc;
      this._data.next(data);
    });
  }

  next() {
    const scoresRef = this.getCollection('scores', ref => ref
      .orderBy('scores', 'desc')
       // Now you can use the latestEntry to query with startAfter
      .startAfter(this.latestEntry)
      .limit(6))
      .subscribe(data => {
        if (data.length) {
          // And save it again for more queries
          this.latestEntry = data[data.length - 1].doc;
          this._data.next(data);
        }
      });
  }

组件

  scores$: Observable<Scores[]>;
  ...
  ngOnInit() {
    this.yourService.first();
    this.scores$ = this.yourService.data;
  }

  nextPage() {
   this.yourService.next();
  }

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