如何将值与 Firebase 实时数据库的子项进行比较？

Question

I would to compare a value with a child of my Firebase Realtime Database but I don't know how to do. The structure of my database is:

This is the code that I wrote:

email = loadPreferences();
mAuth = FirebaseAuth.getInstance();

FirebaseDatabase database = FirebaseDatabase.getInstance();
        final DatabaseReference myRef = database.getReference().child("users");
        myRef.orderByChild("email").equalTo(email).addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {
                if(snapshot.getValue() != null) {
                    //loop through the keys
                    for(DataSnapshot datasnap : snapshot.getChildren()) {

                        if(!email.equalsIgnoreCase("")) {
                            myRef.child("users").child("email").child("address").setValue(getAddress());
                        }
                    }
                }
            }

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

I tried with debugger but when it arrived at "orderByChild()" it skip all and jumps to end. Anyone can help me? Thanks in advance

Answer 1

Data is loaded from Firebase asynchronously, because it needs to be loaded from the cloud. Instead of blocking the app for your users, Firebase instead loads the data in the background and lets your main code continue, which is what you see happening when you step through the code.

Instead of stepping through the code, place a breakpoint on the first line inside onDataChange , and allow the code to run. Then when the data is available, the debugger will hit your breakpoint and you can continue debugging.

You should also implement onCancelled , as you're now ignoring possible problems. At its minimum, this method should be:

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