Read data from Firebase - database

Question

I'm using Firebase for my Android app, I want read datas. In particular I want to select an user with a specific id. When I use the debugger it seems that the code doesn't execute the onDataChange() instruction.
private User readUserById(){
final User u = new User("","","");
Query query = mDatabaseReferences.child("users").orderByChild("id").equalTo(id);
query.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot ds : dataSnapshot.getChildren()){
u.setId(ds.child("id").getValue(User.class).getId());
u.setNumber((ds.child("number").getValue(User.class).getNumber()));
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
return u;
}
private void initFirebase() {
FirebaseApp.initializeApp(this);
mFirebaseDatabase = FirebaseDatabase.getInstance();
mDatabaseReferences = mFirebaseDatabase.getReference();
}
public void sendCode(View v){
id= id.getText().toString();
readUserById();
phoneNumber = phoneText.getText().toString();
if (phoneNumber.equals("") || id.equals("")) {
Toast t = Toast.makeText(this, "Please insert a nickname and a valid phone number", Toast.LENGTH_LONG);
t.show();
} else {
setUpVerificationCallbacks();
PhoneAuthProvider.getInstance().verifyPhoneNumber(
phoneNumber,
60,
TimeUnit.SECONDS,
this,
verificationCallbacks
);
}
// }
}
Using the debugger I've seen that the 'id' value is correct.
I used Firebase documentation for sendCode(), the user registration works correctly, just like the sms sending. I want to check if the nickname already exists, and the value is in the 'id' Textview. I call the sendCode() through a button.
I've tried in this way but doesn't work. Running with the debugger the result of user is null
private User readUserByName(){
final User[] user = {new User()};
DatabaseReference ref = FirebaseDatabase.getInstance().getReference();
ref.child("users").child(nick).addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
if(dataSnapshot.exists()){
user[0] = dataSnapshot.getValue(User.class);
Log.d("Tag", user[0].toString());
}
else
Log.e("Tag","No such user exists");
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
return user[0];
}
This is how I save the User
I've launched the app with the debugger

Answer 1

Assuming that users node is a direct child of your Firebase root, please use the following code:
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference testRef = rootRef.child("users").child("test");
ValueEventListener eventListener = new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
String id = dataSnapshot.child("id").getValue(String.class);
String idName = dataSnapshot.child("idName").getValue(String.class);
String number = dataSnapshot.child("number").getValue(String.class);
Log.d("TAG", id + " / " + idName + " / " + number);
}
#Override
public void onCancelled(DatabaseError databaseError) {}
};
testRef.addListenerForSingleValueEvent(eventListener);
The output will be:
test / f70eb... / number

Answer 2

Assumed that :
node "users" directly under root node.
You already know the id of the user and this id contains all the information under User.class
You only want to read a user, if exists in database.
All the getters and setter exists in User.class and a Public empty constructor exists
Here is how you should do it
DatabaseReference ref = FirebaseDatabase.getInstance().getReference();
ref.child("users").ref(id).addListenerforSingleValueEvent(listener);
And in Listener's OnDataChange(DataSnapshot snap);
if(snap.exists()){
user = snap.getValue(User.class);
Log.d("Tag",user.toString());
}
else
Log.e("Tag","No such user exists");