在firebase android中使用子键获取父名

Question

我试图通过在 android studio 中使用子键“UID”来获取父名称“170002001”。请帮忙。提前致谢 ：）

字符串 uid = user.getUid();

private void getdata(){
    DatabaseReference reference;
    reference = FirebaseDatabase.getInstance().getReference();
    reference.orderByChild("UID").equalTo(uid).addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            for (DataSnapshot childSnapshot: dataSnapshot.getChildren()) {
                keys = childSnapshot.getKey();
                status.setText(keys);
            }
        }
        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {

        }
    });
}

编辑：除“170002001”外，我可以检索所有父名称。:(

Answer 1

把它放在你的onDataChange(DataSnapshot dataSnapshot)听众里面

String parent = dataSnapshot.getKey();

由于firebase将为此管理可能的父键列表，请执行此操作

DatabaseReference reference;
reference = FirebaseDatabase.getInstance.getReference();

reference.addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for (DataSnapshot childSnapshot: dataSnapshot.getChildren()) {
            String parent = childSnapshot.getKey();
            Log.i(TAG,parent);
        }
    }

请注意，此处的引用将是您的"170002001"密钥上方的节点，它是所有这些密钥的父级

编辑：如果您想在每个节点中获取所有 UID，请执行此操作

创建一个 POJO 类来保存该用户 ID

public class UserPojo {


    private String UID;

    public UserPojo(String UID) {
        this.UID = UID;
    }
    public UserPojo() {
    }


    public String getUID() {
        return UID;
    }

    public void setUID(String UID) {
        this.UID = UID;
    }


}

然后像上面一样做同样的事情

   reference.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for (DataSnapshot childSnapshot: dataSnapshot.getChildren()) {
                String parent = childSnapshot.getKey();
                  UserPojo user = childSnapshot.getValue(UserPojo.class);
//get your User ID
 String user = user.getUID();
                Log.i(TAG,parent);
            }
        }