Android，Firebase-尝试检索多个子节点时，数据库仅将单个子节点作为字符串返回

Question

I've just started trying to use Firebase in my Android application. I can write data into the database fine but I'm running into a problem when trying to retrieve data.

My database is structured as below

My method for retrieving the data:

public void getCurrentUserData() {

        FirebaseDatabase database = FirebaseDatabase.getInstance();
        FirebaseUser loggedUser = firebaseAuth.getCurrentUser();
        String uid = loggedUser.getUid();

        DatabaseReference userRef = database.getReference().child("Users").child(uid);

        userRef.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {

                //crashes because user is not a string
                //User user = dataSnapshot.getValue(User.class);

                //works because function is returning first child of uID as a string
                String user = dataSnapshot.getValue().toString();
            }

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

            }
        });

    }

When debugging:

dataSnapshot = "DataSnapshot { key = bio, value = test }"

I was expecting this to return all children contained within uid (bio, dob, firstName, joinDate, lastName, location) and put them into my User object but it actually looks as if its only returning the first child node (bio) as a string.

Why is this happening and how do I retrieve the full set of child nodes?

Any help appreciated. Thanks.

Answer 1

If you want to get all properties of the user, you will either need to create a custom Java class to represent that user, or you will need to read the properties from the individual child snapshots in your own code. For example:

userRef.addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
        String firstName = dataSnapshot.child("firstName").getValue(String.class);
        String lastName = dataSnapshot.child("lastName").getValue(String.class);
        ...
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {
        throw databaseError.toException(); // don't ignore errors
    }
});

Alternatively you can loop over the properties with:

userRef.addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
        for (DataSnapshot propertySnapshot: dataSnapshot.getChildren()) {
            System.out.println(propertySnapshot.getKey()+": "+propertySnapshot.getValue(String.class));
        }
    }