1

我在 Android 中为我的数据库使用 Room，我也在使用 @Relation（基于此：https ://developer.android.com/reference/android/arch/persistence/room/Relation.html ）从关系中获取数据与 ForeinKey 一对多关联的实体。我想要得到的是一个使用@Relation 的 RoomArea 实体的带有 roomAreaNames 的列表。该代码没有编译错误，问题是我只从@Relation 返回的是一个大小为 1 的列表（只有表中的第一个对象）而不是完整列表。

表：

@Entity(
    tableName = "buildings_table",
    indices = [Index("contract_id")],
    foreignKeys = [
        ForeignKey(
            entity = Contract::class,
            parentColumns = ["contract_id"],
            childColumns = ["contract_id"],
            onDelete = ForeignKey.CASCADE)]
)
data class Building(
    @PrimaryKey(autoGenerate = true) @ColumnInfo(name = "building_id")
    val buildingId: Long = 0L,

    @ColumnInfo(name = "contract_id")
    val contractId: Long,

    @ColumnInfo(name = "building_name")
    val buildingName: String)

@Entity(
    tableName = "floors_table",
    indices = [Index("building_id")],
    foreignKeys = [
        ForeignKey(
            entity = Building::class,
            parentColumns = ["building_id"],
            childColumns = ["building_id"],
            onDelete = ForeignKey.CASCADE)]
)
data class Floor(
    @PrimaryKey(autoGenerate = true) @ColumnInfo(name = "floor_id")
    val floor_id: Long = 0L,

    @ColumnInfo(name = "building_id")
    val buildingId: Long,

    @ColumnInfo(name = "level")
    val level: Int
)

@Entity(
    tableName = "rooms_area_table",
    indices = [Index("floor_id")],
    foreignKeys = [
        ForeignKey(
            entity = Floor::class,
            parentColumns = ["floor_id"],
            childColumns = ["floor_id"],
            onDelete = ForeignKey.CASCADE)]
)
data class RoomArea(
    @PrimaryKey(autoGenerate = true) @ColumnInfo(name = "room_area_id")
    val roomAreaId: Long = 0L,

    @ColumnInfo(name = "floor_id")
    val floorId: Long,

    @ColumnInfo(name = "room_area_name")
    val roomAreaName: String
)

道查询：

@Transaction
@Query("SELECT * FROM buildings_table WHERE contract_id = :contractId")
fun getItemsAuditBuilding(contractId: Long): LiveData<List<ItemAuditBuilding>>

这是@Relation（只给我一个大小为 1 的列表）我需要与 buildingId 相关的所有房间区域

data class ItemAuditBuilding(

    @Embedded val building: Building,
    @Relation(
        parentColumn = "building_id",
        entityColumn = "room_area_id",
        entity = RoomArea::class,
        projection = ["room_area_name"]
    )
    var roomAreas: List<String>
)

谢谢你。

4

2 回答 2

0

您正在尝试获取字符串列表。我认为你实际上打算这样做

data class ItemAuditBuilding(
@Embedded val building: Building,
@Relation(
    parentColumn = "building_id",
    entityColumn = "room_area_id",
    entity = RoomArea::class,
    projection = ["room_area_name"]
)
var roomAreas: List<RoomArea>

)

于 2019-10-23T18:51:24.580 回答
0

我希望这可以帮助任何尝试使用 @relation with Room 的人。我的问题的答案基于 2019 年 Android 开发者峰会。这里是 Florina 谈到房间的部分的链接：[ https://www.youtube.com/watch?v=_aJsh6P00c0]。根据视频，我做了以下更改：

我添加了一个连接表：

@Entity(
    primaryKeys = ["building_id", "room_area_id"],
    indices = [Index("room_area_id")]
)
data class RoomAreaWithBuilding(
    @ColumnInfo(name = "building_id")
    val buildingId: Long,
    @ColumnInfo(name = "room_area_id")
    val roomAreaId: Long
)

然后我修改了 ItemAuditBuilding 类

data class ItemAuditBuilding(

    @Embedded val building: Building,

    @Relation(
        parentColumn = "building_id",
        entity = RoomArea::class,
        entityColumn = "room_area_id",
        projection = ["room_area_name"],
        associateBy = Junction(RoomAreaWithBuilding::class)
    )
    val roomAreas: List<String>
)

注意：要使用此代码，您需要使用 Room 2.2，因为associateBy是一项新功能。享受！！！

于 2019-10-27T20:46:16.053 回答