从特定节点 firebase 数据库中检索数据

Question

我正在开发一个 android 应用程序，现在我陷入了从特定节点检索数据的困境，就像我只想从每个节点检索一个值一样。数据库结构如下图。

如何检索 Firebase 数据库创建的第二个唯一 ID？

Answer 1

首先创建一个 POJO 类来获取您想要的值，它的编写方式应该与您在 Firebase 中的编写方式相同。

public class AppointmentsPojo {

    private String appointmentStuts;

    public AppointmentsPojo(){

    }


    public String getAppointmentStuts() {
        return appointmentStuts;
    }

    public void setAppointmentStuts(String appointmentStuts) {
        this.appointmentStuts = appointmentStuts;
    }

}

然后只需在Appointments 内循环以获取每个appointmentStuts

mDatabase.child("Appointments").addListenerForSingleValueEvent(new ValueEventListener() {
  @Override
  public void onDataChange(DataSnapshot dataSnapshot) {
    //Looping inside Appointments to get each appointmentsStuts
    for(DataSnapshot snapshot: dataSnapshot.getChildren()){
    AppointmentsPojo ap = snapshot.getValue(AppointmentsPojo.class);
    //Getting each appointmentStuts
     String appointmentStuts = ap.getAppointmentStuts();
     //To get each father of those appointments 
     String key = snapshot.getKey();

      Log.e("Data: " , "" + appointmentStuts );

       }

  }

  @Override
  public void onCancelled(DatabaseError databaseError) {
    System.out.println("The read failed: " + databaseError.getCode());
  }
});

mDatabase 在哪里

DatabaseReference mDatabase;

mDatabase = FirebaseDatabase.getInstance().getReference();

Answer 2

要仅从第一个对象中获取appointmentStuts 的值，请使用以下代码：

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
Query query = rootRef.child("Appointments").child(PostKey).limitToFirst(1);
ValueEventListener valueEventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            String appointmentStuts = ds.child("appointmentStuts").getValue(String.class);
            Log.d(TAG, appointmentStuts);
        }
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {
        Log.d(TAG, databaseError.getMessage());
    }
};
query.addListenerForSingleValueEvent(valueEventListener);