Get random entries in firebase real-time database - firebase

Question

This is my code to get 5 items from realtime database:
val database = FirebaseDatabase.getInstance()
val brandReference = database.getReference("brandGame").limitToFirst(5)
brandReference.addValueEventListener(object : ValueEventListener {
override fun onDataChange(dataSnapshot: DataSnapshot) {
dataSnapshot.children.forEach {
...
}
}
}
And this is how my real-time database looks like:
What's the best way to get 5 items randomly? I know there isn't a random function in real time database yet.

Answer 1

If you know the number of elements in the brandGame/-reference, you could pick 5 random numbers between 1 and numberOfElements and retrieve those. This would result in multiple calls to the database.
Alternatively, you could download everything from the brandGame/-reference and just pick 5 random elements using pure Kotlin. But then you must download everything in the reference, which could be a lot.
The best option is to set up a cloud function that does the "pick 5 random options"-logic server side. https://firebase.google.com/docs/functions/ But this requires that you write some js :)
As you say, there is no built-in way to get random elements from a reference.

Answer 2

To get a random brand, please use the following code user side:
val rootRef = FirebaseDatabase.getInstance().reference
val brandGameRef = rootRef.child("brandGame")
val valueEventListener = object : ValueEventListener {
override fun onDataChange(dataSnapshot: DataSnapshot) {
val brandCountList = ArrayList<String>()
for (ds in dataSnapshot.children) {
val brand = ds.child("brand").getValue(String::class.java)
brandCountList.add(brand!!)
}
val brandCount = brandCountList.size
val randomNumber = Random().nextInt(brandCount)
val randomBrand = ArrayList<String>()
randomBrand.add(brandCountList.get(randomNumber)) //Add the brand product to list
val arrayAdapter = ArrayAdapter(applicationContext, android.R.layout.simple_list_item_1, randomBrand)
list_view.adapter = arrayAdapter
}
override fun onCancelled(databaseError: DatabaseError) {
//Handle exceptions
}
}
brandGameRef.addListenerForSingleValueEvent(valueEventListener)