Android Firebase database, check if values exist

Question

I'm still learning the basics of android and firebase coding.

I have two problems to tackle:

I need to check if a school from my database exists before continuing.
I need to verify that a username entered by a user isn't already in use (all lowercase).

My database looks like this:

app: {
    school: {
        school: "university one"
        school: "university two"
        school: "university three"
    },
    users: {
        "some-user-uid": {
            school: "university one"
            username: "myname"
        }
    }
}

Thank you.

Your answer is here. http://stackoverflow.com/a/36826793/3145960 — Reaz Murshed, Dec 26 '16 at 02:12
Possible duplicate of [Understanding if data exists in Firebase](http://stackoverflow.com/questions/36826429/understanding-if-data-exists-in-firebase) — Reaz Murshed, Dec 26 '16 at 02:12

Saurabh Padwekar · Answer 1 · 2017-10-24T06:14:45.007

To get your firebase Database reference :

DatabaseReference mDatabase = FirebaseDatabase.getInstance().getReference();

To check if the username exists or not :

String username= "myname" ;
mDatabase.child("app").child("user").child("uid").orderByChild("username").equalTo(username).addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
      if(dataSnapshot!=null && dataSnapshot.getChildren()!=null &&                                         
          dataSnapshot.getChildren().iterator().hasNext()){                     
               //Username exists
             }else {
               //Username does not exist
              }
        }

        @Override
        public void onCancelled(FirebaseError firebaseError) {
               //Error
        }
    });

For school name I wonder how can all the school values have the same key(school)?

Well done, but can you explain how it works and why onCancelled means that username doesn't exist? — Hugo Passos, Oct 18 '17 at 20:30

Android Firebase database, check if values exist

1 Answers1