如何访问firestore中的文档

Question

我有一个 firebase 数据库，顶部有一个 users 节点。例如，我想获取该节点的第一个子节点。我正在尝试以这种方式访问​​，但我说：

TypeError: "this.users[0] is undefined"

export class FirebaseService {
  user: Observable<User | null>
  userCollection: AngularFirestoreCollection<User>;
  users: Observable<User[]>;

  getUserByEmail(email) {
     this.userCollection = this.afs.collection('users');
     this.users = this.userCollection.valueChanges();
     let a = this.users[0].name;

我已经看了很多教程，但我找不到错误的原因

Answer 1

需要订阅valueChanges

this.userCollection.valueChanges().subscribe((item) => {
   this.users = item;
   console.log(this.users[0].name)
})