如何将Firestore子集合中的数据添加到列表中？

Question

FirebaseFirestore _firestore = FirebaseFirestore.instance;
  CollectionReference _userRef = FirebaseFirestore.instance.collection('users');
Future getFriends() async {
    List<Map> info = [];
    await _firestore
        .collection('friends')
        .doc('lUb3VEzLQsqxxEhwO3nU')
        .collection('friends')
        .get()
        .then((QuerySnapshot querySnapshot) {
      querySnapshot.docs.forEach((element) async {
        print("hello " + element.id.toString());
        await _userRef.doc(element.id).get().then((value) {
          print("lalala" + value.data().toString());
          info.add(value.data());
        });
      });
    });
    print(info.toString());
  }

如果有人能在这里帮助我，我会非常喜欢它：）

Answer 1

问题似乎是将子集合转换为列表。尝试以下操作：

FirebaseFirestore _firestore = FirebaseFirestore.instance;
  CollectionReference _userRef = FirebaseFirestore.instance.collection('users');
Future getFriends() async {
    List<Map> info = [];
    await _firestore
        .collection('friends')
        .doc('lUb3VEzLQsqxxEhwO3nU')
        .collection('friends')
        .get()
        .then((QuerySnapshot querySnapshot) {
      querySnapshot.docs.forEach((element) async {
        print("hello " + element.id.toString());
        await _userRef.doc(element.id).get().then((value) {
          print("lalala" + value.data().toString());
          info.add(Map(Map.fromMap(value.data())));
        });
      });
    });
    print(info.toString());
  }

Answer 2

我认为问题是您根本没有返回Future中的任何内容。

试试这个

FirebaseFirestore _firestore = FirebaseFirestore.instance;
  CollectionReference _userRef = FirebaseFirestore.instance.collection('users');
Future getFriends() async {
    List<Map> info = [];
    await _firestore
        .collection('friends')
        .doc('lUb3VEzLQsqxxEhwO3nU')
        .collection('friends')
        .get()
        .then((QuerySnapshot querySnapshot) {
      querySnapshot.docs.forEach((element) async {
        print("hello " + element.id.toString());
        await _userRef.doc(element.id).get().then((value) {
          print("lalala" + value.data().toString());
          info.add(value.data());
        });
      });
    });
    return info ;
  }

Answer 3

您可以通过snapshot.data.documents访问文档，然后您可以获得这样的文档ID

var doc= snapshot.data.documents;
var docId=doc[index].documentID 

FirebaseFirestore.instance
              .collection('dishes')
              .doc(docId)
              .collection('ingredients')
              .snapshots(),