How to update an existing value in the Firebase Realtime Database?

Question

I would to update an existing value in my Firebase Realtime Database. I have tried several ways but none have worked. Anyone know how can I fix it? I attach the structure of the db if it can be useful and the code I have written so far. Thanks in advance to everyone

FirebaseDatabase database = FirebaseDatabase.getInstance();
final DatabaseReference myRef = database.getReference().child("users");

myRef.orderByChild("email").equalTo(email).addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot snapshot) {
        if(snapshot.getValue() != null) {
            //loop through the keys
            Map<String, Object> hashMap = new HashMap<>();
            for(DataSnapshot datasnap : snapshot.getChildren()) {

                if(datasnap.child("email").getValue().toString().equals(email)) {

                    hashMap.put("address", "TEST1");

                    myRef.child(email).updateChildren(hashMap).addOnSuccessListener(new OnSuccessListener() {
                        @Override
                        public void onSuccess(Object o) {
                            Toast.makeText(LocationActivity.this, "Data successfully update",
                                    Toast.LENGTH_SHORT).show();
                        }
                    });
                }
            }
        }
    }

    @Override
    public void onCancelled(@NonNull DatabaseError error) {
        throw error.toException();
    }
});

Answer 1

FirebaseFirestore ff = FirebaseFirestore.getInstance();
            ff.collection("myCollection")
                    .document(myAuth.getCurrentUser().getUid())
                    .update("field",value)
                    .addOnCompleteListener(new OnCompleteListener<Void>() {
                        @Override
                        public void onComplete(@NonNull Task<Void> task) {
                            if(task.isSuccessful()){
                                //for example Toast.makeText(context,getString(R.string.user_updated),Toast.LENGTH_SHORT).show();
                            }
                        }
                    });

Answer 2

You're updating the wrong location in the database, which means that either the write is now showing up in the screenshot or it is rejected (which your code doesn't handle).

To update the address of the child node you're looping over:

myRef.orderByChild("email").equalTo(email).addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot snapshot) {
        for(DataSnapshot datasnap : snapshot.getChildren()) {
            datasnap.child("address").getRef().setValue("TEST1").addOnSuccessListener(new OnSuccessListener() {
                @Override
                public void onSuccess(Object o) {
                    Toast.makeText(LocationActivity.this, "Data successfully update",
                            Toast.LENGTH_SHORT).show();
                }
            });
        }
    }

    @Override
    public void onCancelled(@NonNull DatabaseError error) {
        throw error.toException();
    }
});

The key change here is that I call getRef() on the snapshot, to get a reference to that specific location in the database.

You'll note that I also removed the two conditions, since neither of them had any effect on the outcome.