Firebase Error: "Expected a List while deserializing, but got a class java.util.HashMap"

Question

I had a structure in my database that worked perfectly, but then I add the following node to my database and since then I'm getting this error. If I delete the "commentList" node it works again. Why would it change from a list to a Hashmap?

My db structure. It worked before adding that "commentList"

The code responsible for this: code

Here the log error:

com.google.firebase.database.DatabaseException: Expected a List while deserializing, but got a class java.util.HashMap
    at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToParameterizedType(com.google.firebase:firebase-database@@16.0.5:233)
    at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToType(com.google.firebase:firebase-database@@16.0.5:176)
    at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.access$100(com.google.firebase:firebase-database@@16.0.5:47)
    at com.google.firebase.database.core.utilities.encoding.CustomClassMapper$BeanMapper.deserialize(com.google.firebase:firebase-database@@16.0.5:580)
    at com.google.firebase.database.core.utilities.encoding.CustomClassMapper$BeanMapper.deserialize(com.google.firebase:firebase-database@@16.0.5:550)
    at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertBean(com.google.firebase:firebase-database@@16.0.5:420)
    at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToClass(com.google.firebase:firebase-database@@16.0.5:214)
    at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToType(com.google.firebase:firebase-database@@16.0.5:178)
    at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.access$100(com.google.firebase:firebase-database@@16.0.5:47)
    at com.google.firebase.database.core.utilities.encoding.CustomClassMapper$BeanMapper.deserialize(com.google.firebase:firebase-database@@16.0.5:580)
    at com.google.firebase.database.core.utilities.encoding.CustomClassMapper$BeanMapper.deserialize(com.google.firebase:firebase-database@@16.0.5:550)
    at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertBean(com.google.firebase:firebase-database@@16.0.5:420)
    at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToClass(com.google.firebase:firebase-database@@16.0.5:214)
    at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToType(com.google.firebase:firebase-database@@16.0.5:178)
    at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToParameterizedType(com.google.firebase:firebase-database@@16.0.5:247)
    at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToType(com.google.firebase:firebase-database@@16.0.5:176)
    at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertToCustomClass(com.google.firebase:firebase-database@@16.0.5:101)
    at com.google.firebase.database.DataSnapshot.getValue(com.google.firebase:firebase-database@@16.0.5:239)
    at com.example.xandi.whib.MainActivity$3.onDataChange(MainActivity.java:236)
    at com.google.firebase.database.core.ValueEventRegistration.fireEvent(com.google.firebase:firebase-database@@16.0.5:75)
    at com.google.firebase.database.core.view.DataEvent.fire(com.google.firebase:firebase-database@@16.0.5:63)
    at com.google.firebase.database.core.view.EventRaiser$1.run(com.google.firebase:firebase-database@@16.0.5:55)
    at android.os.Handler.handleCallback(Handler.java:790)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:164)
    at android.app.ActivityThread.main(ActivityThread.java:6626)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:811)

What is causing this and how would I fix this?

Answer 1

I know it's a bit late, but I'll post it for others who encounter the same issue. Firebase real-time database does not store collections in lists but HashMaps. Your model property should be more like this:

var commentList: HashMap<String, String>? = null

Answer 2

You must be sure that the firebase object is array, not map, like that: firebase

I've had the same problem, the solution was check the type of object, directly in firebase database and change Map(HashMap) to Array(List)