Flutter：在一个集合中检索用户并在另一个集合中进行审阅并合并数据的问题

时间：2019-02-04 20:12:41

标签： dart flutter google-cloud-firestore

我有两个要从中检索数据的集合：User集合和Review集合。我在Review集合中有一个“ user_id”字符串，该字符串引用了用户文档ID。

我正在检索Review数据，然后尝试检索User数据并合并两者，以便使用User的名称。

我有一个Firestore提供程序类，一个Review Bloc和一个User Bloc。代码如下：

firestore_provider.dart

static FirestoreProvider instance = FirestoreProvider();
Firestore _firestore = Firestore.instance;

Future<List<Review>> retrieveAllReviewsByProductId(String productId) async {
    final List<Review> reviewList = [];
    final QuerySnapshot result = await _firestore
        .collection('reviews')
        .where('product_id', isEqualTo: productId)
        .getDocuments();
    final List<DocumentSnapshot> docs = result.documents;

    if (docs.length > 0) {
      docs.forEach((review) {
        _firestore
            .collection('users')
            .document(review.data['user_id'])
            .get()
            .then((user) {
          reviewList.add(Review(
              id: review.documentID,
              user: user.data['username'],
              body: review.data['body'],
              score: double.parse(review.data['score'])));
        });
      });
    }
    return reviewList;
  }

review_bloc.dart

final _reviews = PublishSubject<List<Review>>();
Observable<List<Review>> get allReviewsForProduct => _reviews.stream;

retrieveReviewsForProduct(String productId) async {
    final List<Review> reviewList = await FirestoreProvider.instance
        .retrieveAllReviewsByProductId(productId);
    _reviews.sink.add(reviewList);
  }

product_review_card.dart

class ProductReviewCard extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    ReviewBloc reviewBloc = BlocProvider.of<ReviewBloc>(context);
    // reviewBloc.retrieveReviewsForProduct(productId)

    return CardBase(
      child: StreamBuilder<List<Review>>(
        stream: reviewBloc.allReviewsForProduct,
        builder: (context, AsyncSnapshot<List<Review>> snapshot) {
          if (snapshot.hasData) {
            return Material(child: _buildReviews(snapshot.data));
          } else if (snapshot.hasError) {
            return Text('Failed ${snapshot.error}');
          }
          return Center(child: CircularProgressIndicator());
        },
      ),
    );
  }

  Widget _buildReviews(List<Review> reviews) {
    return Column(
      crossAxisAlignment: CrossAxisAlignment.start,
      children: <Widget>[
        Row(
          children: <Widget>[
            Text(
              'Reviews',
              style: TextStyle(
                  fontSize: AppConstants.PRODUCT_REVIEW_TITLE_FONT_SIZE,
                  fontWeight: FontWeight.bold),
            ),
          ],
          mainAxisAlignment: MainAxisAlignment.spaceBetween,
        ),
        SizedBox(height: 20),
        Column(
          children: 
          reviews.map((review) {
            return UserReview(review: review);
          }).toList(),
        ),
      ],
    );
  }
}

我希望检索用户并将其注入到Review模型对象中，但会收到错误消息


I/flutter (14653): retrieved all products: (AxFHaKkQJmSDBoEDT6Qe, HutbbzH1mwdAAy3OVzW5, zHUx3c4dG9GTYUxjMWTJ)
I/flutter (14653): retrieved all products: (AxFHaKkQJmSDBoEDT6Qe, HutbbzH1mwdAAy3OVzW5, zHUx3c4dG9GTYUxjMWTJ)
E/flutter (14653): [ERROR:flutter/shell/common/shell.cc(184)] Dart Error: Unhandled exception:
E/flutter (14653): NoSuchMethodError: The method '[]' was called on null.
E/flutter (14653): Receiver: null
E/flutter (14653): Tried calling: []("username")
E/flutter (14653): #0      Object.noSuchMethod (dart:core/runtime/libobject_patch.dart:50:5)
E/flutter (14653): #1      FirestoreProvider.retrieveAllReviewsByProductId.<anonymous closure>.<anonymous closure> 
package:tokd/…/providers/firestore_provider.dart:100
E/flutter (14653): #2      _RootZone.runUnary (dart:async/zone.dart:1379:54)
E/flutter (14653): #3      _FutureListener.handleValue (dart:async/future_impl.dart:129:18)
E/flutter (14653): #4      Future._propagateToListeners.handleValueCallback (dart:async/future_impl.dart:642:45)
E/flutter (14653): #5      Future._propagateToListeners (dart:async/future_impl.dart:671:32)
E/flutter (14653): #6      Future._complete (dart:async/future_impl.dart:476:7)
E/flutter (14653): #7      _SyncCompleter.complete (dart:async/future_impl.dart:51:12)
E/flutter (14653): #8      _AsyncAwaitCompleter.complete (dart:async/runtime/libasync_patch.dart:28:18)
E/flutter (14653): #9      _completeOnAsyncReturn (dart:async/runtime/libasync_patch.dart:295:13)
E/flutter (14653): #10     DocumentReference.get (file:///home/stephen/flutter/.pub-cache/hosted/pub.dartlang.org/cloud_firestore-0.9.0/lib/src/document_reference.dart)
E/flutter (14653): <asynchronous suspension>
E/flutter (14653): #11     FirestoreProvider.retrieveAllReviewsByProductId.<anonymous closure> 
package:tokd/…/providers/firestore_provider.dart:96
E/flutter (14653): #12     List.forEach (dart:core/runtime/libgrowable_array.dart:278:8)
E/flutter (14653): #13     FirestoreProvider.retrieveAllReviewsByProductId 
package:tokd/…/providers/firestore_provider.dart:92
E/flutter (14653): #14     _RootZone.runUnary (dart:async/zone.dart:1379:54)
E/flutter (14653): #15     _FutureListener.handleValue (dart:async/future_impl.dart:129:18)
E/flutter (14653): #16     Future._propagateToListeners.handleValueCallback (dart:async/future_impl.dart:642:45)
E/flutter (14653): #17     Future._propagateToListeners (dart:async/future_impl.dart:671:32)
E/flutter (14653): #18     Future._complete (dart:async/future_impl.dart:476:7)
E/flutter (14653): #19     _SyncCompleter.complete (dart:async/future_impl.dart:51:12)
E/flutter (14653): #20     _AsyncAwaitCompleter.complete (dart:async/runtime/libasync_patch.dart:28:18)
E/flutter (14653): #21     _completeOnAsyncReturn (dart:async/runtime/libasync_patch.dart:295:13)
E/flutter (14653): #22     Query.getDocuments (file:///home/stephen/flutter/.pub-cache/hosted/pub.dartlang.org/cloud_firestore-0.9.0/lib/src/query.dart)
E/flutter (14653): #23     _RootZone.runUnary (dart:async/zone.dart:1379:54)
E/flutter (14653): #24     _FutureListener.handleValue (dart:async/future_impl.dart:129:18)
E/flutter (14653): #25     Future._propagateToListeners.handleValueCallback (dart:async/future_impl.dart:642:45)
E/flutter (14653): #26     Future._propagateToListeners (dart:async/future_impl.dart:671:32)
E/flutter (14653): #27     Future._complete (dart:async/future_impl.dart:476:7)
E/flutter (14653): #28     _SyncCompleter.complete (dart:async/future_impl.dart:51:12)
E/flutter (14653): #29     _AsyncAwaitCompleter.complete (dart:async/runtime/libasync_patch.dart:28:18)
E/flutter (14653): #30     _completeOnAsyncReturn (dart:async/runtime/libasync_patch.dart:295:13)
E/flutter (14653): #31     MethodChannel.invokeMethod (package:flutter/src/services/platform_channel.dart)
E/flutter (14653): #32     _RootZone.runUnary (dart:async/zone.dart:1379:54)
E/flutter (14653): #33     _FutureListener.handleValue (dart:async/future_impl.dart:129:18)

Flutter Doctor表现良好

flutter doctor -v
[✓] Flutter (Channel stable, v1.0.0, on Linux, locale en_CA.UTF-8)
    • Flutter version 1.0.0 at /home/stephen/flutter
    • Framework revision 5391447fae (10 weeks ago), 2018-11-29 19:41:26 -0800
    • Engine revision 7375a0f414
    • Dart version 2.1.0 (build 2.1.0-dev.9.4 f9ebf21297)

[✓] Android toolchain - develop for Android devices (Android SDK 28.0.3)
    • Android SDK at /home/stephen/Android/Sdk
    • Android NDK location not configured (optional; useful for native profiling
      support)
    • Platform android-28, build-tools 28.0.3
    • Java binary at: /home/stephen/android-studio/jre/bin/java
    • Java version OpenJDK Runtime Environment (build
      1.8.0_152-release-1248-b01)
    • All Android licenses accepted.

[✓] Android Studio (version 3.3)
    • Android Studio at /home/stephen/android-studio
    • Flutter plugin version 32.0.1
    • Dart plugin version 182.5124
    • Java version OpenJDK Runtime Environment (build
      1.8.0_152-release-1248-b01)

[✓] VS Code (version 1.30.2)
    • VS Code at /usr/share/code
    • Flutter extension version 2.22.3

[✓] Connected device (1 available)
    • Android SDK built for x86 • emulator-5554 • android-x86 • Android 9 (API
      28) (emulator)

• No issues found!

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