com.google.firebase.database.DatabaseException: Serializing Arrays is not supported, please use Lists instead

Question

I am trying to persist a custom object using the following code:

DatabaseReference databaseReference = FirebaseDatabase.getInstance().getReference();
DatabaseReference curWorkoutExercisesRef = databaseReference.child("workouts")
            .child(mCurrentWorkout.getId())
            .child("workoutExercises");

WorkoutExercise we = new WorkoutExercise(exercise);
curWorkoutExercisesRef.push().setValue(we);

Here's my object:

public class WorkoutExercise {

    private String id;
    private Exercise exercise;

    public WorkoutExercise() {}

    // getters, setters, other methods 
    // ...
}

public class Exercise {

    private String id;
    private String title;

    private List<BodyPart> bodyParts;

    public Exercise() {}

    // getters, setters, other methods 
    // ...
}

public class BodyPart {

    private String id;
    private String name;

    public BodyPart() {}

    // getters, setters, other methods 
    // ...
}

And every time I am getting this error - com.google.firebase.database.DatabaseException: Serializing Arrays is not supported, please use Lists instead. My objects don't contain any arrays so this error looks quite confusing. I found a way to fix this error - everything works fine if I add the @Exclude annotation to the bodyParts list from my Exercise class but it is obviously not what I am trying to achieve.

So seems that Firebase is unable to persist objects containing inner lists? Are there any straightforward workarounds or best practices here? Thanks!

P.S. I am using firebase-database:9.2.1

Answer 1

I've managed to find the reason causing this crash. I installed the app on another device running Android 5.x and Firebase threw a much less confusing exception there:

com.google.firebase.database.DatabaseException: No properties to serialize found on class android.graphics.Paint$Align

It appeared that Firebase (unlike Gson) tries to serialize all possible getters even though they don't have direct connection with global variables (class members / fields), in my particular case one of my objects contained a method returning Drawable - getDrawable(). Obviously, Firebase doesn't know how to convert drawable into json.

Interesting moment (probably a bug in Firebase SDK): on my older device running Android 4.4.1 I still get my original exception in the same project and configuration:

Caused by: com.google.firebase.database.DatabaseException: Serializing Arrays is not supported, please use Lists instead

Answer 2

In case this helps others that are receiving the same error, I was getting the same error and the solution ended up being the following for me:

Changing:

databaseReference.child("somechild").setValue(etName.getText());

To:

databaseReference.child("somechild").setValue(etName.getText().toString());

As @fraggjkee points out, Firebase attempts to serialize getters, and this was the similar issue here with firebase attempting to serialize the result of the .getText().

Hope this helps others!

Answer 3

Add @Exclude to the functions that FB tries to interpret, like those that return a Drawable.

@Exclude
public Drawable getUnitColorImage(){
    return TextDrawable.builder().buildRound("", prefColor);
}

Answer 4

I had a similar problem, I was trying to use groovy instead of Java, I guess that groovy is generating other get methods for me. I converted my domain class from Pogo (src/main/groovy) to Pojo (src/main/java) and now all is working well