Firestore: How to get random documents in a collection

Question

It is crucial for my application to be able to select multiple documents at random from a collection in firebase.

Since there is no native function built in to Fireb

Answer 1

Unlike rtdb, firestore ids are not ordered chronologically. So using Auto-Id version described by Dan McGrath is easily implemented if you use the auto-generated id by the firestore client.

      new Promise(async (resolve, reject) => {
        try {
          let randomTimeline: Timeline | undefined;
          let maxCounter = 5;
          do {
            const randomId = this.afs.createId(); // AngularFirestore
            const direction = getRandomIntInclusive(1, 10) <= 5;
            // The firestore id is saved with your model as an "id" property.
            let list = await this.list(ref => ref
              .where('id', direction ? '>=' : '<=', randomId)
              .orderBy('id', direction ? 'asc' : 'desc')
              .limit(10)
            ).pipe(take(1)).toPromise();
            // app specific filtering
            list = list.filter(x => notThisId !== x.id && x.mediaCounter > 5);
            if (list.length) {
              randomTimeline = list[getRandomIntInclusive(0, list.length - 1)];
            }
          } while (!randomTimeline && maxCounter-- >= 0);
          resolve(randomTimeline);
        } catch (err) {
          reject(err);
        }
      })