要使子表中的更新查询反映在父表中,需要使用观察者模式。具体来说,需要在父表的Dao中使用@Relation注释来声明父表和子表之间的关系,并使用LiveData来获取父表,然后就可以使用observe方法观察子表的更改并更新父表。以下是示例代码:
@Entity(tableName = "parent_table")
data class Parent(
@PrimaryKey val id: Int,
val name: String
)
@Entity(tableName = "child_table", foreignKeys = [
ForeignKey(entity = Parent::class, parentColumns = ["id"], childColumns = ["parentId"])
])
data class Child(
@PrimaryKey val id: Int,
val name: String,
val parentId: Int
)
data class ParentWithChildren(
@Embedded val parent: Parent,
@Relation(
parentColumn = "id",
entityColumn = "parentId"
)
val children: List
)
@Dao
interface ParentDao {
@Query("SELECT * FROM parent_table")
fun getParentWithChildren(): LiveData>
}
// 在Activity中观察数据的更改并更新UI界面
val parentDao = database.parentDao()
parentDao.getParentWithChildren().observe(this, Observer { parentsWithChildren ->
// 更新UI界面
})