Room error: Cannot figure out how to save this field into database. You can consider adding a type converter for it

Question

I tried to set a type converter for city at the entity, but there is still the error as in the question title. Let's see at my entity:

@Entity(tableName = "users")
data class UserEntity(
    @PrimaryKey(autoGenerate = true)
    val id: Int = 0,
    val name: String,
    val city: City?
)

Yes, someone can tell me that type converter should be applied to field city like this:

@TypeConverter(CityConverter::class)
val city: City?

but it is also not works))
Below is my database, City and CityConverter

@Database(entities = [UserEntity::class], version = 1, exportSchema = false)
// As you can see, I apply type converter here
@TypeConverters(CityConverter::class)
abstract class MyDatabase : RoomDatabase() {
    abstract val dao: MyDao

    companion object {
        @Volatile
        private var instance: MyDatabase? = null

        fun getInstance(context: Context): MyDatabase {
            var currentInstance = instance
            if (currentInstance == null) {
                currentInstance =
                    Room.databaseBuilder(context, MyDatabase::class.java, "mydb").build()
                instance = currentInstance
                return currentInstance
            }
            return currentInstance
        }
    }

}

City:

data class City(
    val name: String
)

And converter:

class CityConverter {

    private val jsonAdapter = Moshi.Builder()
        .addLast(KotlinJsonAdapterFactory())
        .build()
        .adapter(City::class.java)

    @TypeConverter
    fun cityToString(city: City?): String {
        return city?.let { jsonAdapter.toJson(it) } ?: ""
    }

    @TypeConverters
    fun stringToCity(json: String?): City? {
        return json?.let { jsonAdapter.fromJson(json) }
    }
}

I did all as in the documentation, but it is not work(

Answer 1

Try replacing:

    @TypeConverters
    fun stringToCity(json: String?): City? {
        return json?.let { jsonAdapter.fromJson(json) }
    }

with, by removing the s from @TypeConverters:

    @TypeConverter
    fun stringToCity(json: String?): City? {
        return json?.let { jsonAdapter.fromJson(json) }
    }