Android Room无法弄清楚如何将此字段保存到数据库中

Question

我尝试通过房间持久库将"保存值"保存到数据库。我的SettingsValueModelConverter缺失了错误。我如何保存SettingsKeyContract对象最佳方法？

logcat：

SettingsModel
Error:(14, 1) error: Cannot figure out how to save this field into database. You can consider adding a type converter for it.

代码：

object SETTING_CONS{
    const val TABLE = "Content_Setting"
    const val ID    = "uid"
    const val KEY   = "key"
    const val VALUE = "value"
}
class SettingsValueModel(var value: SettingsKeyContract)
class SettingsValueModelConverter {
    @TypeConverter
    fun fromString(value: String): SettingsKeyContract = Gson().fromJson(value, object : TypeToken<SettingsKeyContract>() {}.type)
    @TypeConverter
    fun fromModel(value: SettingsKeyContract): String = Gson().toJson(value)
}
@Entity(tableName = SETTING_CONS.TABLE)
class SettingsModel(@ColumnInfo(name = SETTING_CONS.KEY) @SETTINGS var key: String,
                    @ColumnInfo(name = SETTING_CONS.VALUE) var value: SettingsValueModel) {
    @ColumnInfo(name = SETTING_CONS.ID)
    @PrimaryKey(autoGenerate = true)
    var uid: Int = 0
}
@Dao
interface SettingsDao {
    @Query("SELECT * FROM ${SETTING_CONS.TABLE} WHERE ${SETTING_CONS.ID} = :key")
    fun get(@SETTINGS key: String): LiveData<SettingsModel>
    @get:Query("SELECT * FROM ${SETTING_CONS.TABLE}")
    val all: LiveData<MutableList<SettingsModel>>
    @Insert(onConflict = OnConflictStrategy.REPLACE)
    fun insert(model: SettingsModel): Long
    @Insert(onConflict = OnConflictStrategy.REPLACE)
    fun insertAll(vararg models: SettingsModel): LongArray
    @Query("DELETE FROM ${SETTING_CONS.TABLE} WHERE ${SETTING_CONS.KEY} = :key")
    fun delete(@SETTINGS key: String)
    @Query("DELETE FROM ${SETTING_CONS.TABLE}")
    fun clear()
}

interface SettingsKeyContract { val key: String }
interface TypeSettingsKeyContract<out T : Any> : SettingsKeyContract { val default: T }
sealed class SETTING(override val key: String) : SettingsKeyContract {
    object FIRST_LAUNCH_DATE : SETTING("first_launch_date"), TypeSettingsKeyContract<Long> { override val default = 0L }
}

Answer 1

您在哪里定义数据库？您应该可以选择在那里指定要使用的转换器，例如：

@Database(entities = arrayOf(SettingsModel::class) , version = 1, exportSchema = false)
@TypeConverters(SettingsValueModelConverter::class)
abstract class AppDatabase: RoomDatabase() {
    abstract fun SettingsDao(): SettingsDao
}