房间错误:无法确定如何将此字段保存到数据库中。您可以考虑为其添加类型转换器

我试着为设置一个类型转换器 city 在实体上,但仍然存在问题标题中的错误。让我们看看我的实体:

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

是的,有人可以告诉我类型转换器应该应用于字段 城市 这样地:

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

但它也不起作用))
下面是我的数据库, City 和 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
        }
    }

}

城市

data class City(
    val name: String
)

和转换器:

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) }
    }
}

我按照文档中的内容做了所有操作,但这不起作用(