java - Android:从子集合中获取字段值

Question

有没有办法从子集合中获取数据？下面是我的数据库的结构，对于每个用户，只会在“userinfo”子集合中创建一个文档来存储用户名和电子邮件。

我试图从 Firestore 获取“用户名”和“电子邮件”值，然后将这些值设置为如下字符串:

字符串用户名 = ?字符串电子邮件 = ?

"main"(root_collection)
            |
            |=>userid1(auto-generated)
                         |                  
                         |=>"userinfo"(sub-collection)=>documentID(auto)=>username: mary
                         |                                              =>email:mary@gmail.com
                         |                                             
                         |                            
                         |=>"emotions"(sub-collection)=>documentID(auto)=>happy: true
                                                                        =>sad:false
                                                                        =>depressed:false

我从其他问题中读到了一些其他答案，说可以使用

检索字段值

String value = documentSnapshot.getString("field");

但是我还是不知道怎么办？我写了一些东西，但我不知道如何获取值。

 FirebaseAuth mAuth = FirebaseAuth.getInstance();
        String userId = Objects.requireNonNull(mAuth.getCurrentUser()).getUid();

        FirebaseFirestore db = FirebaseFirestore.getInstance();
        CollectionReference userRef = db.collection("main").document(userId).collection("userinfo");

        userRef.get().addOnSuccessListener(new OnSuccessListener<QuerySnapshot>() {
            @Override
            public void onSuccess(QuerySnapshot queryDocumentSnapshots) {
                //get the value
                String value = queryDocumentSnapshots.getDocuments("username"); // how ??
            }
        }).addOnFailureListener(new OnFailureListener() {
            @Override
            public void onFailure(@NonNull Exception e) {
                Toast.makeText(SettingsActivity.this, e.getMessage(), Toast.LENGTH_LONG).show();
            }
        });

还有一个对象类 UserInfo

import java.io.Serializable;

public class UserInfo implements Serializable {

    private String email, username;

    public UserInfo() {}

    public UserInfo(String email, String username) {
        this.email = email;
        this.username = username;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }
}

请帮忙，非常感谢。

Answer 1

Is there a way to get data from sub-collection?

是的，有。要获取该数据，您必须循环访问结果，如以下代码行所示:

userRef.get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
    @Override
    public void onComplete(@NonNull Task<QuerySnapshot> task) {
        if (task.isSuccessful()) {
            for (QueryDocumentSnapshot document : task.getResult()) {
                String value = document.getString("username");
                Log.d("TAG", value);
            }
        } else {
            Log.d(TAG, "Error getting documents: ", task.getException());
        }
    }
});

logcat 中的结果将是:

mary