angular/fire get next item in collection using startAfter

Question

I am having trouble getting the next item in a collection using angular/fire.

The error I am getting is:

Error: Function startAfter() called with invalid data. Unsupported field value: a custom AngularFirestoreDocument object

Based on these Firebase docs I think startAfter() wants a DocumentSnapshot but I don't know how to convert AngularFirestoreDocument to DocumentSnapshot and whilst the angular/fire docs mention startAfter they do not give any code examples.

Here's my problem code. I want the first document in the collection after the video document.

getNextVideo$(id: string, group: string): Observable<IVideo> {

  const video: AngularFirestoreDocument<IVideo> = this.afs.doc<IVideo>(`videos/${id}`)

  const collection: AngularFirestoreCollection<IVideo> = this.afs.collection<IVideo>('videos', ref => {
    return ref
      .where('group', '==', group)
      .where('flowPlayerProcessed', '==', true)
      .orderBy('timeCreated')
      .startAfter(video) // <<<<< ERROR IS HERE
      .limit(1)
  })

  return collection.valueChanges().pipe(
    map((videos: IVideo[]) => videos.length ? videos[0] : null)
  )
}

Answer 1

OK this rather verbose monstrosity works

getNextVideo$(id: string, group: string): Observable<IVideo> {

  const video: AngularFirestoreDocument<IVideo> = this.afs.doc<IVideo>(`videos/${id}`)

  return video.snapshotChanges().pipe(
    switchMap((videoSnapshotAction: Action<DocumentSnapshot<IVideo>>) => {

      const videoSnapshot: DocumentSnapshot<IVideo> = videoSnapshotAction.payload

      const collection: AngularFirestoreCollection<IVideo> = this.afs.collection<IVideo>('videos', ref => {
        return ref
          .where('group', '==', group)
          .where('flowPlayerProcessed', '==', true)
          .orderBy('timeCreated')
          .startAfter(videoSnapshot)
          .limit(1)
      })
      return collection.valueChanges().pipe(
        map((videos: IVideo[]) => videos.length ? videos[0] : null)
      )
    })
  )
}