Error when using TypeConverter with Room: Cannot figure out how to save this field into database

Question

I get this error:

error: Cannot figure out how to save this field into database. You can consider adding a type converter for it. private final java.util.List<com.example.Detail.Stat> stats = null;

I can't figure it out. I have Added the typeconverter to the database, but still get this error. Any ideas what I do wrong?

Entity:

@Entity
data class Detail(
    @PrimaryKey val id: Int,
    val stats: List<Stat>,
    val types: List<String>

){
    data class Stat(
        val baseStat: Int,
        val stat: String
    )
}

Typeconverter:

@ProvidedTypeConverter
class StatConverter @Inject constructor(
    private val moshi: Moshi
){
    @TypeConverter
    fun fromJson(value: String): List<Detail.Stat>? {
        val listType = Types.newParameterizedType(List::class.java, Detail.Stat::class.java)
        val adapter: JsonAdapter<List<Detail.Stat>> = moshi.adapter(listType)
        return adapter.fromJson(value)
    }
    @TypeConverter
    fun toJson(type: List<Detail.Stat>?): String {
        val listType = Types.newParameterizedType(List::class.java, Detail.Stat::class.java)
        val adapter: JsonAdapter<List<Detail.Stat>> = moshi.adapter(listType)
        return adapter.toJson(type)
    }
}

Database:

@Database(entities = [Detail::class], version = 1, exportSchema = true)
@TypeConverters(StatConverter::class)
abstract class Database : RoomDatabase() {

    abstract fun detailDao(): DetailDao

    companion object{
        const val DATABASE = "database"
    }

}

DI module where room is provided:

@Singleton
    @Provides
    fun provideAppDatabase(
        application: Application,
        statConverter: StatConverter
    ): Database {
        return Room
            .databaseBuilder(application, Database::class.java,
                Database.DATABASE
            )
            .addTypeConverter(statConverter)
            .fallbackToDestructiveMigration()
            .build()
    }

EDIT:

The typeconverter code works fine with the other field (List) in the entity, but not with List.

Answer 1

Apparently, something about your nested data class is causing problems, and so moving Stat out from being nested in Detail helped.

If you have the time, you might try creating a scrap project that illustrates the problem, then file an issue on the issue tracker, attaching that project as a demonstration of the problem. I don't see anything that quite matches, but there are a lot of issues, so perhaps I missed it.