带有子查询的 AngularFireStore return 集合

Question

我有以下功能

getParticipations(
    meetingId: string
  ): Observable<Participation[]> {
    return this.meetingCollection
      .doc(meetingId)
      .collection<ParticipationDto>('participations')
      .snapshotChanges()
      .pipe(
        map(actions =>
          actions.map(m => {
            const participationDto = m.payload.doc.data() as ParticipationDto;
            const id = m.payload.doc.id;
            return new Participation(id, participationDto.vart, null);
          })
        )
      );
  }

在 participationDto 中有一个文档引用，我想获取该文档以便 return 一个对象（参与）与引用文档的映射。

类似

  getParticipations(
    meetingId: string
  ): Observable<Participation[]> {
    return this.meetingCollection
      .doc(meetingId)
      .collection<ParticipationDto>('participations')
      .snapshotChanges()
      .pipe(
        map(actions =>
          actions.map(m => {
            const participationDto = m.payload.doc.data() as ParticipationDto;
            const id = m.payload.doc.id;
            return this.participantCollection.doc(participationDto.participant.id).get().pipe(
              map(pp => {
                return new Participation(id, participationDto.vart, pp.data() as Participant);
              })
            );
          })
        )
      );
  }

但是 return 是 Observable<Observable<Participation>[]> 我可能需要合并、映射或类似的东西，但我没有找到使我的 Observable 丰富我的对象映射并保持我的 Observable<Participation[]>

的正确方法

感谢帮助

Answer 1

您可以尝试在 Observable 的内部列表上使用 forkJoin 并将外部映射切换为 switchMap。

     getParticipations(
    meetingId: string
  ): Observable<Participation[]> {
    return this.meetingCollection
      .doc(meetingId)
      .collection<ParticipationDto>('participations')
      .snapshotChanges()
      .pipe(
        switchMap(actions =>
          forkJoin(actions.map(m => {
            const participationDto = m.payload.doc.data() as ParticipationDto;
            const id = m.payload.doc.id;
            return this.participantCollection.doc(participationDto.participant.id).get().pipe(
              map(pp => {
                return new Participation(id, participationDto.vart, pp.data() as Participant);
              })
            ));
          })
        )
      );
  }

Answer 2

您需要使用 mergeMap 而不是 map

如下所示

getParticipations(
    meetingId: string
  ): Observable<Participation[]> {
    return this.meetingCollection
      .doc(meetingId)
      .collection<ParticipationDto>('participations')
      .snapshotChanges()
      .pipe(
        mergeMap(actions =>
          actions.map(m => {
            const participationDto = m.payload.doc.data() as ParticipationDto;
            const id = m.payload.doc.id;
            return this.participantCollection.doc(participationDto.participant.id).get().pipe(
              map(pp => {
                return new Participation(id, participationDto.vart, pp.data() as Participant);
              })
            );
          })
        )
      );
  }


getParticipations(
    meetingId: string
  ): Observable<Participation[]> {
    return this.meetingCollection
      .doc(meetingId)
      .collection<ParticipationDto>('participations')
      .snapshotChanges()
      .pipe(
        map(actions =>
          actions.map(m => {
            const participationDto = m.payload.doc.data() as ParticipationDto;
            const id = m.payload.doc.id;
            return this.participantCollection.doc(participationDto.participant.id).get().pipe(
              mergeMap(pp => {
                return new Participation(id, participationDto.vart, pp.data() as Participant);
              })
            );
          })
        )
      );
  }

（因为它很复杂且嵌套并且没有提供 stackblitz，所以我无法验证解决方案，但是如果它不起作用请告诉我删除此答案）

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