文档在我的 flutter 应用程序中的 firebase 中的特定集合中发生更改

Question

我已经实现了逻辑，但是当侦听器在仅更新一个文档或添加或删除它后触发时，整个文档都会获取给我，但他们有什么方法可以仅获取更新的文档。

这里是提供商

class OfferProvider with ChangeNotifier {
  final OffersService _offerService = OffersService();
  List<Offer> _offers = [];

  List<Offer> get offers => _offers;

  OfferProvider() {
    _listenToOffers();
  }

  void _listenToOffers() {
    _offerService.getOffers().listen((offersData) {
      _offers = offersData;
      notifyListeners();
    });
  }
}

这是与 firestore 对话的服务

class OffersService {
  final FirebaseFirestore _firestore = FirebaseFirestore.instance;

  /// Retrieves a stream of offers from the Firestore database.
  ///
  /// Returns a stream of lists of `Offer` objects, where each list represents a snapshot of the 'offers' collection.
  ///
  /// The stream is updated in real-time as the data in the Firestore database changes.
  Stream<List<Offer>> getOffers() {
    return _firestore.collection('offers').snapshots().map((snapshot) {
      return snapshot.docs.map((doc) => Offer.fromFirestore(doc)).toList();
    });
  }
}

提前致谢

我尝试添加以下代码并获取更新的快照，但使用从 firestore 收到的数据，所有文档都会再次获取：

提供商

 void _listenToOffers() {
    _offerService.getOffers().listen((snapshot) {
      for (var change in snapshot.docChanges) {
        switch (change.type) {
          case DocumentChangeType.added:
            // Handle added documents
            _offers.add(Offer.fromFirestore(change.doc));
            break;
          case DocumentChangeType.modified:
            // Handle modified documents
            int index =
                _offers.indexWhere((offer) => offer.id == change.doc.id);
            if (index != -1) {
              _offers[index] = Offer.fromFirestore(change.doc);
            }
            break;
          case DocumentChangeType.removed:
            // Handle removed documents
            _offers.removeWhere((offer) => offer.id == change.doc.id);
            break;
        }
      }
      notifyListeners();
    });
  }

服务

class OfferService {
  final FirebaseFirestore _firestore = FirebaseFirestore.instance;

  Stream<QuerySnapshot> getOffers() {
    return _firestore
        .collection('offers')
        .where('activated', isEqualTo: true)
        .snapshots();
  }
}

Answer 1

整个文档都给我了
...
所有文档都用它再次获取

Firestore客户端实际上只从数据库服务器获取修改后的文档。但 API 会生成包含已修改和未修改文档的查询快照。如果您想区分它们，查看

docChanges

数组中的更改类型（正如 Doug 评论的那样）。