No setter/getter for Firebase objects

This is my Java class:

public class OnlineMatch{

private FacebookUser firstplayer;
private FacebookUser secondplayer;


public OnlineMatch(){

}


public OnlineMatch(FacebookUser firstplayer, FacebookUser secondplayer) {
this.firstplayer = firstplayer;
this.secondplayer = secondplayer;
}

public FacebookUser getFirstplayer() {
return firstplayer;
}

public void setFirstplayer(FacebookUser firstplayer) {
this.firstplayer = firstplayer;
}

public FacebookUser getSecondplayer() {
return secondplayer;
}

public void setSecondplayer(FacebookUser secondplayer) {
this.secondplayer = secondplayer;
}

}

I can create objects correctly and uploaded to Firebase. The db structure is as follow:
[![Screenshot taken from firebase panel control][1]][1]

[1]:

Then I try to print the values of my OnlineMatch objects (Kotlin code):

val match = dataSnapshot.child("multiplayer").getValue(OnlineMatch::class.java)
if(match!=null){
System.out.println(match)
}

Here I get this output on the Android Studio console:

9548-19548/app.simone W/ClassMapper: No setter/field for -KqV44f4FUxV8ZDuqL4Y found on class app.simone.multiplayer.model.OnlineMatch

08-01 19:14:38.816 19548-19548/app.simone W/ClassMapper: No setter/field for -KqV3sAPXPcYrtr61cDy found on class app.simone.multiplayer.model.OnlineMatch

08-01 19:14:38.816 19548-19548/app.simone W/ClassMapper: No setter/field for -KqV2BGH7Z-Y9RxnPGpt found on class app.simone.multiplayer.model.OnlineMatch

Your code is asking for *everything* under `multiplayer`, which includes all of the OnlineMatch objects you pushed there previously. You can see from the error message that it's trying to find a setter or field for the push ID `-KqV44f4FUxV8ZDuqL4Y` that it found just under `multiplayer` If you want to get a single OnlineMatch object, you're going to have to dig into the objects in the push IDs under `multiplayer`. So this should give you something:

dataSnapshot.child("multiplayer/-KqV44f4FUxV8ZDuqL4Y").getValue(OnlineMatch::class.java)

In any event, you'll need to have the push ID of your choice, or discover them from the children of the snapshot and build a new snapshot from that child.

Doug Stevenson, your answer was useful to me.
I created an array of strings where I save the key and then I iterate over the child for each specific key:

override fun onDataChange(dataSnapshot: DataSnapshot) {

// Get Post object and use the values to update the UI
val match = dataSnapshot.children
var keysArray = KeysHandler()
if(match!=null){
// saving keys into an array
for (data in match){
keysArray.addToList(data.key)
}

// saving an OnlineMatch object into another array
repeat(keysArray.list.size){ i->
val onlineMatch = dataSnapshot.child(keysArray.getElement(i)).getValue(OnlineMatch::class.java)!!
requestsUsers.add(onlineMatch)

}

// updating GUI
updateRequests()
}

}