Infinite cycle on Firebase with Kotlin

Question

So, my app does is a QR code scanner that adds the QR id to the current user UID. I first verify if the user already did that scan; if not, that id is added to the firebase table; otherwise, it will create that table. This is my code:

private fun infoAdd(str2: String, view: View) {
        val  currentUser = auth.currentUser?.uid
        val postReference = FirebaseDatabase.getInstance().getReference("organsUsers")
        val dbView = postReference.child(currentUser.toString())
        val postListener = object : ValueEventListener {
            override fun onDataChange(snapshot: DataSnapshot) {
                val org = snapshot.child("uOrgans")
                if (org != null) {
                    val post = org.getValue(String::class.java)
                    dbView.child("uOrgans").setValue("$post,$str2")
                } else {
                    dbView.child("uOrgans").setValue(str2)
                }
            }

            override fun onCancelled(databaseError: DatabaseError) {
            }
        }
        dbView.addValueEventListener(postListener)
    }

The str2 it's the string of the QR id.

This is what happens to Firebase:

Please Help!!!!

Alex Mamo · Accepted Answer · 2021-03-05T19:46:08.260

1

I first verify if the user already did that scan; if not, that id is added to the firebase table; otherwise, it will create that table.

It doesn't make any sense because in both cases you are "setting" the value of str2 into the database, that's why you see that behavior of highlighting that operation in yellow. Because a Firebase Realtime Database is a NoSQL database and is structured as pairs of keys and values, every node is a Map, which means that when using a setValue() operation, the old value is replaced with the new one.

If you want to check if the value of uOrgans exists, then update it for example, please use the following lines of code:

val uid = FirebaseAuth.getInstance().currentUser!!.uid
val rootRef = FirebaseDatabase.getInstance().reference
val uidRef = rootRef.child("organsUsers").child(uid)
val valueEventListener = object : ValueEventListener {
    override fun onDataChange(snapshot: DataSnapshot) {
        val org = snapshot.child("uOrgans")
        if(org.exists()) {
            val post = org.getValue(String::class.java)
            dbView.getRef().updateChildren(mapOf("uOrgans" to "$post,$str2")) //Update it
            Log.d("TAG", $post,$str2)
        } else {
            uidRef.child("uOrgans").setValue(str2)
        }
    }

    override fun onCancelled(databaseError: DatabaseError) {
        Log.d("TAG", databaseError.getMessage()) //Don't ignore potential errors!
    }
}
uidRef.addListenerForSingleValueEvent(valueEventListener)

If doesn't exist, the str2 is added to the database.

One thing to mention, if uOrgans doesn't exist, none of its parents (organsUsers and the UID) nodes will not exist.

edited Mar 05 '21 at 19:46

answered Mar 05 '21 at 14:21

Alex Mamo

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I tried, but the updateChildren only accept Map<>, not String...it's giving me an error. – Guilherme Faure Mar 05 '21 at 19:34
Yes, you're right. Sorry, my bad. Instead of passing a String, pass a Map like in my updated answer. – Alex Mamo Mar 05 '21 at 19:46
Thanks! It worked! Can you help me in one more thing? How can i verify if tha id already exists? If it already exists, i dont need to add it. – Guilherme Faure Mar 05 '21 at 20:17
Good to hear that. Sure, please check my answer from this [post](https://stackoverflow.com/questions/47893328/checking-if-a-particular-value-exists-in-the-firebase-database/47893879). – Alex Mamo Mar 06 '21 at 09:06
I already saw your post, but it doesn't work...i've tried some diferent ways. Is there a way to find a string on that variable? – Guilherme Faure Mar 07 '21 at 18:29
What do you mean by "find a string on that variable"? – Alex Mamo Mar 08 '21 at 09:05
I already figured out. I just splitted that string I got from database. One more thing...do you have any experience with recycler view on fragments? Because I've tried many ways and none of them worked... – Guilherme Faure Mar 08 '21 at 11:07
I think this [repo](https://github.com/alexmamo/FirebaseApp-Clean-Architecture-MVVM) might help. – Alex Mamo Mar 08 '21 at 11:25
I just saw, but i didn't found the fragment and the recyclerview. I'm also new at this, so I can't really translate from java to kotlin. Do you think i should do a new question? – Guilherme Faure Mar 08 '21 at 12:43
@GuilhermeFaure Yes, a new question would be more helpful. – Alex Mamo Mar 08 '21 at 12:47
I've already posted a new question...Will you check it out? – Guilherme Faure Mar 08 '21 at 13:29
@GuilhermeFaure I've seen it and already answer it. – Alex Mamo Mar 08 '21 at 13:43

Infinite cycle on Firebase with Kotlin

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