Question

我有一个包含当前观看电影的每个用户的 ID 的观众子集合 viewers 的电影集合。

我需要你的帮助来绑定来自 Firestore 的用户流。做到这一点：

我从子集合中获取所有查看者 ID
我使用 whereIn 创建了一个查询过滤器，以检查我当前获取的用户是否在查看者列表中问题是我什么也拿不到。由于 snapshot() 什么都没有了。我已经使用这种方法和 map 迭代查询快照，但在这种情况下没有任何作用

希望有人能帮助我！ :)

Stream<List<UserModel>> viewerStream(String movieId) {
    List<String> viewersId = [];
    List<UserModel> viewers = [];

    _firestore
        .collection(MOVIECOLLECTION)
        .doc(movieId)
        .collection(VIEWERS)
        .get().then((value) {
      value.docs.forEach((element) {
        viewersId.add(element.id);
      }); //works fine, I get my userIds

      if (viewersId == null || viewersId.length == 0) return null;

     return _firestore
          .collection(USERSCOLLECTION)
          .where(FieldPath.documentId, whereIn: viewersId)
          .snapshots()//since here, nothing works
          .map((query) {
        query.docs.forEach((element) {
          viewers.add(UserModel.fromDocumentSnapshot(documentSnapshot: element));
        });
      });
      return viewers;
    });
  }```

Answer 1

试试这个

    _firestore
    .collection(USERSCOLLECTION)
    .where(FieldPath.documentId, whereIn: viewersId)
    .snapshots()
    .listen((event) => onViewersChange(event.docChanges));

对于文档的每次更改

  onViewersChange(List<DocumentChange<Map<String, dynamic>>> docChanges) {
    docChanges.forEach((docChange) {
      if (docChange.type == DocumentChangeType.added) {
        docChange.doc.data(); // Add to your Viewers List
      } else if (docChange.type == DocumentChangeType.modified) {
        docChange.doc.data(); // Replace this data to the existing data in Viewers List
      } else if (docChange.type == DocumentChangeType.removed) {
        docChange.doc.data(); //Remove this data from your viewerList
      }
    });
  }

Answer 2

我试过你给我看的东西，但现在我的听众总是返回空：

The method 'listen' was called on null.
Receiver: null
Tried calling: listen(Closure: (List<UserModel>) => List<UserModel>)

这是我的代码：

Stream<List<UserModel>> viewersStream(String movieId) {
    List<String> viewersId = [];
    List<UserModel> viewers = [];

    onViewersChange(List<DocumentChange> docChanges, List<UserModel> viewersList) {
      docChanges.forEach((docChange) {
        if (docChange.doc != null && docChange.doc.exists) {
          if (docChange.type == DocumentChangeType.added) {
            viewersList.add(UserModel.fromDocumentSnapshot(
                documentSnapshot: docChange.doc));
            docChange.doc.data(); // Add to your Viewers List
          } else if (docChange.type == DocumentChangeType.modified) {
            docChange.doc
                .data(); // Replace this data to the existing data in Viewers List
            viewersList.forEach((element) {
              if (element.id == docChange.doc.id) {
                element = UserModel.fromDocumentSnapshot(
                    documentSnapshot: docChange.doc);
              }
            });
          } else if (docChange.type == DocumentChangeType.removed) {
            docChange.doc.data();
            viewersList.removeWhere((element) => (element.id ==
                docChange.doc.id)); //Remove this data from your viewerList
          }
        }
      });
    }

    _firestore
        .collection(MOVIECOLLECTION)
        .doc(viewerId)
        .collection(VIEWERS)
        .get()
        .then((value) {
      value.docs.forEach((element) {
        viewersId.add(element.id);
      });

      _firestore
          .collection(USERSCOLLECTION)
          .where(FieldPath.documentId, whereIn: viewersId)
          .snapshots()
          .listen((event) {
        onViewersChange(event.docChanges, viewers);
        return viewers;
      });
    });
  }

使用快照方法在颤振中获取 Firestore 问题

2 个答案: