Check if firebase child has a specific value

Question

I have a app chat based on firebase database and I want to know if a particular value is already stored.

According to the above structure how can I prevent two equal values (in red) from being inserted into the same child (blue)?

EDIT

I solved this problem as follows: 1) I changed the push values of each node by unique username; 2) I checked the duplicate values with the code below:

FirebaseDatabase.getInstance().getReference().child("friend").child(value_in_blue)
        .addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                if(!dataSnapshot.hasChild(username)) {
                    //value does not exists
                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {
            }
        });

Thank you Frank van Puffelen and Jins Lukose for giving me guidance on this issue.

There is no atomic way to prevent duplicate **values** in a tree. The solution is typically to have an additional data structure where the values are used as the keys, because the child keys in a node are by definition guaranteed to be unique. See https://stackoverflow.com/q/39912201, https://stackoverflow.com/a/25328654, https://stackoverflow.com/a/20291163, https://stackoverflow.com/a/35244705 — Frank van Puffelen, Nov 13 '18 at 14:48

score 2 · Answer 1 · answered Nov 13 '18 at 11:36

2

Firebase provides hasChild() method to check value for child exist or not for pirticuler child. You can refer link for more details

answered Nov 13 '18 at 11:36

score 1 · Answer 2 · answered Nov 13 '18 at 11:49

1

Try this

fdbRefer.child("give your value").addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
if(dataSnapshot.exist() {
//comes here if exit
}
else {
//if not exist
}
}
});

answered Nov 13 '18 at 11:49

Jins Lukose

699
6
19

This prevents any value from being inserted! – afazolo Nov 13 '18 at 12:11
@afazolo before inserting next value use this. i have used this same in a project – Jins Lukose Nov 13 '18 at 12:16
Okay. But once I enter a value I can not insert another one! – afazolo Nov 13 '18 at 12:42
@afazolo i think you have some logic mistake – Jins Lukose Nov 14 '18 at 04:13
Maybe. I'll do some more testing with your approach. Thank you. – afazolo Nov 14 '18 at 09:21
I've tried using FirebaseDatabase.getInstance().getReference().child(idFriend), where idFriend is the value in red of my question, with no success. Should I try .child("friend"/ + idFriend)? – afazolo Nov 14 '18 at 13:05

Check if firebase child has a specific value

2 Answers2