如何从 flutter 中的 firestore 文档字段获取数据？

Question

我正在尝试在我的 flutter-app 中测试 firestore，但我无法真正按预期加载数据。

这就是我获取数据的方式：

 Firestore.instance
        .collection('Test')
        .document('test')
        .get()
        .then((DocumentSnapshot ds) {
      // use ds as a snapshot

      print('Values from db: $ds');
    });

和打印语句 output：flutter：来自 db 的值：“DocumentSnapshot”的实例。

我也试过以下，但没有成功：

Firestore.instance.collection('Test').document('test').get().then((data) {
  // use ds as a snapshot

  if (data.documentID.length > 0) {
    setState(() {
      stackOver = data.documentID;
      print(stackOver);
    });
  }
});

Output 这里只是 documentID-name..

那么，我怎样才能从 firestore 中获取字段值呢？

最好的祝福！

Answer 1

尝试这个：

final String _collection = 'collectionName';
final Firestore _fireStore = Firestore.instance;

getData() async {
  return await _fireStore.collection(_collection).getDocuments();
}

getData().then((val){
    if(val.documents.length > 0){
        print(val.documents[0].data["field"]);
    }
    else{
        print("Not Found");
    }
});

Answer 2

我遇到了类似的问题并以这种方式解决了它：

Stream<DocumentSnapshot> provideDocumentFieldStream() {
    return Firestore.instance
        .collection('collection')
        .document('document')
        .snapshots();
}

之后，我使用 StreamBuilder 来使用上面创建的方法：

StreamBuilder<DocumentSnapshot>(
    stream: provideDocumentFieldStream(),
    builder: (BuildContext context, AsyncSnapshot<DocumentSnapshot> snapshot) {
        if (snapshot.hasData) {
            //snapshot -> AsyncSnapshot of DocumentSnapshot
            //snapshot.data -> DocumentSnapshot
            //snapshot.data.data -> Map of fields that you need :)

            Map<String, dynamic> documentFields = snapshot.data.data;
            //TODO Okay, now you can use documentFields (json) as needed

            return Text(documentFields['field_that_i_need']);
        }
    }
)

Answer 3

我正在尝试在flutter-app中测试firestore，但是我无法真正按预期加载数据。

这就是我获取数据的方式：

 Firestore.instance
        .collection('Test')
        .document('test')
        .get()
        .then((DocumentSnapshot ds) {
      // use ds as a snapshot

      print('Values from db: $ds');
    });

以及打印语句输出：flutter：来自db的值：'DocumentSnapshot'的实例。

我还尝试了以下操作，但没有成功：

Firestore.instance.collection('Test').document('test').get().then((data) {
  // use ds as a snapshot

  if (data.documentID.length > 0) {
    setState(() {
      stackOver = data.documentID;
      print(stackOver);
    });
  }
});

这里的输出仅是documentID名称。

那么，如何从Firestore获取字段值？

此致！

Answer 4

空安全码：

• 一次读取数据：

   var collection = FirebaseFirestore.instance.collection('Test'); var docSnapshot = await collection.doc('test').get(); if (docSnapshot.exists) { Map<String, dynamic>? data = docSnapshot.data(); // You can then retrieve the value from the Map like this: var value = data?['your_field']; }

• 持续监听数据：

   var collection = FirebaseFirestore.instance.collection('Test'); collection.doc('test').snapshots().listen((docSnapshot) { Map<String, dynamic>? data = docSnapshot.data(); if (docSnapshot.exists) { Map<String, dynamic>? data = docSnapshot.data(); // You can then retrieve the value from the Map like this: var value = data?['your_field']; } });

Answer 5

我在 Firestore 数据库中有一个用户列表，我需要提取用户名信息

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_auth/firebase_auth.dart';

FirebaseAuth firebaseAuth = FirebaseAuth.instance;

class Database {      
  static String? userName;
  
  static void showDisplayName() async {
    var collection = FirebaseFirestore.instance.collection('users');
    //userUid is the current auth user
    var docSnapshot = await collection.doc(userUid).get();

    Map<String, dynamic> data = docSnapshot.data()!;

    userName = data['displayName'];
  }
}

然后你可以调用Database.userName来获取字符串值

这是我的 Firestore 示例

Answer 6

有2种方式：

1.StreamBuilder

当你想不断地监听变化，并希望数据在没有热重载/重启的情况下得到更新

2.未来建造者

当你只想获取文档一次，而不需要一直监听文档的变化时。

---

StreamBuilder

1. 多份文件

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: StreamBuilder<QuerySnapshot>(
          stream: FirebaseFirestore
                  .instance.
                  .collection('users') // 👈 Your desired collection name here
                  .snapshots(), 
          builder: (BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot) {
            if (snapshot.hasError) {
              return const Text('Something went wrong');
            }
            if (snapshot.connectionState == ConnectionState.waiting) {
              return const Text("Loading");
            }
            return ListView(
                children: snapshot.data!.docs.map((DocumentSnapshot document) {
              Map<String, dynamic> data =
                  document.data()! as Map<String, dynamic>;
              return ListTile(
                title: Text(data['fullName']), // 👈 Your valid data here
              );
            }).toList());
          },
        ),
      ),
    );
  }

2. 单一文件

 @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: StreamBuilder<DocumentSnapshot<Map<String, dynamic>>>(
          stream:  FirebaseFirestore
                   .instance
                   .collection('users')
                   .doc(FirebaseAuth.instance.currentUser!.uid) // 👈 Your document id change accordingly
                   .snapshots(), 
          builder:
              (BuildContext context, AsyncSnapshot<DocumentSnapshot> snapshot) {
            if (snapshot.hasError) {
              return const Text('Something went wrong');
            }
            if (snapshot.connectionState == ConnectionState.waiting) {
              return const Text("Loading");
            }
            Map<String, dynamic> data =
                snapshot.data!.data()! as Map<String, dynamic>;
            return Text(data['fullName']); // 👈 your valid data here
          },
        ),
      ),
    );
  }

---

未来建造者

1. 多份文件

@override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
          child: FutureBuilder<QuerySnapshot>(
        future: FirebaseFirestore
                .instance
                .collection('users') // 👈 Your collection name here
                .get(), 
        builder: (_, snapshot) {
          if (snapshot.hasError) return Text('Error = ${snapshot.error}');
          if (snapshot.connectionState == ConnectionState.waiting) {
            return const Text("Loading");
          }
          return ListView(
              children: snapshot.data!.docs.map((DocumentSnapshot document) {
            Map<String, dynamic> data = document.data()! as Map<String, dynamic>;
            return ListTile(
              title: Text(data['avatar']), // 👈 Your valid data here
            );
          }).toList());
        },
      )),
    );
  }

2. 单一文件

 @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
          child: FutureBuilder<DocumentSnapshot<Map<String, dynamic>>>(
        future: FirebaseFirestore.instance
            .collection('users')
            .doc(FirebaseAuth.instance.currentUser!.uid)  // 👈 Your document id change accordingly
            .get(),
        builder: (_, snapshot) {
          if (snapshot.hasError) return Text('Error = ${snapshot.error}');
          if (snapshot.connectionState == ConnectionState.waiting) {
            return const Text("Loading");
          }
          Map<String, dynamic> data = snapshot.data!.data()!;
          return Text(data['fullName']); //👈 Your valid data here
        },
      )),
    );
  }