FirebaseDatabase 和 FirebaseFirestore 数据处理和检索数据的问题

Question

My query is that I want to save some data in Firebase Realtime Database such that I will be able to call the data. Keeping in mind that users should be able to call the data even if they reinstall the app and each user will have a specific child.

I am trying to make an app where the user will enter or save data to firebase and display it on the App, however, the issue is that I am not having an Idea on how to retrieve the data from firebase.

The data which I am going to retrieve is the ItemName which I have saved inside

child(uid).child(ItemName);

each user will save their data with different uid inside different ItemName.

The thing is that how will I retrieve the ItemName for each user since the ItemName will be different so I will not have any data of the ItemName for a particular user. If I save the ItemName in SharedPreferences I will be able to retrieve it, however, if the user, formate their phone or uninstall and reinstall the app then SharedPreference data will be removed, SO HOW WILL I RETRIVE THE ITEMNAME data from Firebase for a particular user to display it.

MY CODE example:

String email= mAuth.getCurrentUser().getUid();
dbFirestore= FirebaseFirestore.getInstance();
userReference= FirebaseDatabase.getInstance().getReference().child("Users").child(itemName);

Is there any method or function which retrieve the data without specifying the Child pathname like default path if we redirect the path towards there like

databaseReference = FirebaseDatabase.getInstance().getReference().child(uid).child(""); 

something like that. or is there any other way to do it.

Answer 1

To those values, without knowing the name of the intermediate node, please use the following lines of code:

String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference uidRef = rootRef.child(uid);
ValueEventListener valueEventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            String friedChicken = ds.getKey();
            String foodType = ds.child("food_TYPE").getValue(String.class);
            Log.d("TAG", friedChicken + "/" + foodType);
        }
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {
        Log.d("TAG", databaseError.getMessage()); //Don't ignore errors!
    }
};
uidRef.addListenerForSingleValueEvent(valueEventListener);

The output in the logcat will be:

Fried Chicken / Non-Veg

In the same way I got the value of food_TYPE , you can also get the others.

Answer 2

You can do the following

DatabaseReference ref = FirebaseDatabase.getInstance().getReference().child(uid).child("Fried Chicken");
ref.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
        String foodType = dataSnapshot.child("food_TYPE").getValue().toString();
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {

    }
});