我想加载实体子列表,但是我希望避免进行2个查询。
我考虑在TypeConverter内部执行查询,但我真的不知道这是否是一个好主意。
我的实体:
@Entity
class Region(
@PrimaryKey(autoGenerate = true)
var id: Int = 0,
var name: String = "",
var locales: List<Locale> = listOf())
@Entity(foreignKeys = arrayOf(ForeignKey(
entity = Region::class,
parentColumns = arrayOf("id"),
childColumns = arrayOf("regionId"),
onDelete = CASCADE,
onUpdate = CASCADE
)))
class Locale(
@PrimaryKey(autoGenerate = true)
var id: Int = 0,
var regionId: Int = 0,
var name: String = "")
DAOs :
@Dao
interface RoomRegionDao{
@Insert
fun insert(region: Region)
@Delete
fun delete(region: Region)
@Query("select * from region")
fun selectAll(): Flowable<List<Region>>
}
@Dao
interface RoomLocaleDao{
@Insert
fun insert(locale: Locale)
@Query("select * from locale where regionId = :arg0")
fun selectAll(regionId: Int): List<Locale>
}
数据库:
@Database(entities = arrayOf(Region::class, Locale::class), version = 1)
@TypeConverters(RoomAppDatabase.Converters::class)
abstract class RoomAppDatabase : RoomDatabase() {
abstract fun regionDao(): RoomRegionDao
abstract fun localeDao(): RoomLocaleDao
inner class Converters {
@TypeConverter
fun toLocales(regionId: Int): List<Locale> {
return localeDao().selectAll(regionId)
}
@TypeConverter
fun fromLocales(locales: List<Locale>?): Int {
locales ?: return 0
if (locales.isEmpty()) return 0
return locales.first().regionId
}
}
}
无法使用内部类作为转换器类,因此它无法工作。
- 这是一个好方法吗?
- 当我执行
RoomRegionDao.selectAll
时,如何在区域实体中自动加载“本地化列表”?