在Firebase Android中使用子项键获取父名称

Question

I am trying to get parent name "170002001" by using child key "UID" in android studio. Please help. Thanks in advance :)

String 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) {

        }
    });
}

Edit: Except "170002001" i am able to retrieve all parent name. :(

Answer 1

Place this inside your onDataChange(DataSnapshot dataSnapshot) listener

String parent = dataSnapshot.getKey();

Since firebase will manage a list of possible parent keys for that , do this

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);
        }
    }

note that reference here will be the node up above your "170002001" key, which is the parent of all those keys

Edit: If you want to get all UID inside each of those nodes do this

Create a POJO class to hold that user 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;
    }


}

then just do the same like above

   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);
            }
        }