How to check for existing data in Firebase?

Question

above is my firebase node tree. here is my code:

private fun attemptAdd(){
    var focus: View? = null
    var cancel: Boolean = false
    var prefix: String  = prePrefView.text.toString() + prefText.text.toString()
    var sp: SimPrefix

    //checks for the length of the input
    if(prefText.length()<2){
        prefText.error = "invalid length"
        cancel = true
        focus = prefText
    }

    mDatabaseReference.child("simnumbers")
            .orderByChild("simPref")
            .equalTo(prefix)
            .addListenerForSingleValueEvent(object : ValueEventListener{
                override fun onDataChange(dataSnapshot: DataSnapshot) {
                    dataSnapshot.children.forEach {
                        sp = it.getValue(SimPrefix::class.java)!!
                        if(sp.simCard.equals(prefix)){ //checks if there is already a node with the same data
                            prefText.error = "already exists"
                            cancel = true
                            focus = prefText
                        }
                    }
                }

                override fun onCancelled(p0: DatabaseError?) {

                }
            })

    if(cancel){
        focus?.requestFocus()
    }
    else{ //if all is valid, proceed to the next method.
        addPrefix()
    }
}

What I assume here is that it doesn't seem to enter the listener since it always proceeds to the next method allowing the user to enter the same existing data.

[Have you seen this question? The answers here might help you.](https://stackoverflow.com/questions/47893328/checking-if-a-particular-value-exists-in-the-firebase-database?rq=1) — Christan Shane Plaza, May 02 '18 at 06:38

score 1 · Answer 1 · answered May 02 '18 at 06:38

I provide java code you can change into kotlin and also put your condition in to onDatachange method..

     Query query1=reference.child(reference.getKey()).child("simnumbers").orderByChild("simPref").equalTo(prefix);
    query1.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            // here place your condition
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });

do I also need to put the condition in an iteration ? – ronan May 02 '18 at 07:29 — ronan, May 02 '18 at 07:29

score 0 · Answer 2 · edited Jun 20 '20 at 09:12

Try the following to check if data exists:

  mDatabaseReference.child("simnumbers")
        .orderByChild("simPref")
        .equalTo(prefix)
        .addListenerForSingleValueEvent(object : ValueEventListener{
            override fun onDataChange(dataSnapshot: DataSnapshot) {
                    if(dataSnapshot.exists()){
                dataSnapshot.children.forEach {
                    sp = it.getValue(SimPrefix::class.java)!!
                       }
                    }
                }
            }

            override fun onCancelled(p0: DatabaseError?) {

            }
        })

The datasnapshot is at simnumbers, then it will check if that snapshot exists in the database and if the child simPref is equal to the value provided

public boolean exists ()

Returns true if the snapshot contains a non-null value.

more info here:

https://firebase.google.com/docs/reference/android/com/google/firebase/database/DataSnapshot.html#exists()

actually I got it, I just removed the .equalTo() and moved the if(cancel){}else{} inside the onDataChanged() but outside of the iteration. But still, thanks! — ronan, May 02 '18 at 08:48
@ronan since the answer helped you, please upvote it and mark it as correct, thank you! — Peter Haddad, May 08 '18 at 07:09

How to check for existing data in Firebase?

2 Answers2