firebase - 在 flutter 中使用 withConverter 获取 Firestore 文档引用字段的数据

Question

我有约会与学生和老师的集合为reference与其他字段一起输入。

我想使用 CollectionReference.withConverter 获取约会列表.但是由于引用字段，我无法获取它们。

示例代码:

FirebaseFirestore.instance.collection('appts').withConverter<Appointment>(
      fromFirestore: (snapshot, _) {
        Map<String, dynamic> appt = snapshot.data()!;

        Student student = await appt['student'] // <---- Error as await is NOT allowed here
                .get()
                .then((studentSnapshot) => Student.fromMap(studentSnapshot.data()!));

        return Appointment.fromMap(
          snapshot.data()!
            ..['id'] = snapshot.id
            ..['student'] = student,
        );
      },
      toFirestore: (appointment, _) => ...,
    );

await不允许作为 withConverter<Appointment>期待 fromFirestore返回 Appointment对象而不是 Future<Appointment>

没有await , 我会得到 Future<Student> ，并且不确定如何将完整文档映射到Student 类型。

有没有 Flutter 的 Firestore 自动获取引用文档而不是我手动获取它们？

Answer 1

这里有一些示例可以帮助您处理他们的文档。

在 flutter 中使用 withCoverter带转换器现在，您可以在各个地方使用 withConverter 来更改此类型:

DocumentReference.withConverter:
final modelRef = FirebaseFirestore
    .instance 
    .collection('models') 
    .doc('123') 
    .withConverter<Model>( 
        fromFirestore: (snapshot, _) => Model.fromJson(snapshot.data()!), 
        toFirestore: (model, _) => model.toJson(), 
);

DocumentReference.withConverter (公共(public)文档)

CollectionReference.withConverter:

final modelsRef = FirebaseFirestore
      .instance
      .collection('models')
      .withConverter<Model>( fromFirestore: (snapshot, _) => Model.fromJson(snapshot.data()!), 
      toFirestore: (model, _) => model.toJson(), 
);

CollectionRefence.withConverter (公共(public)文档)

查询.withConverter:

final personsRef = FirebaseFirestore
      .instance 
      .collection('persons') 
      .where('age', isGreaterThan: 0) 
      .withConverter<Person>( fromFirestore: (snapshot, _) => Person.fromJson(snapshot.data()!), 
      toFirestore: (model, _) => model.toJson(), 
);

Query.withCoverter (公共(public)文档)

这里还有firebase、flutter的一些文档:

https://firebase.flutter.dev/docs/firestore/usage/ https://firebase.google.com/docs/reference/js/v8/firebase.firestore.CollectionReference