Android房间内的3路交叉表

Question

我正在努力实现以下目标

我有以下实体

@Entity(tableName = "workspace_table")
data class WorkSpace(
    @PrimaryKey
    val workSpaceId:Long,
    .....
)

@Entity(tableName = "widget_table")
data class Widget(
    val widgetId:Long,
    .......
)

@Entity(tableName = "feed_table")
data class Feed(
    val feedId:Long,
    .......
)

我从 3 表中想要的是下面的 POJO

data class MergedData(
@Embedded workSpace:WorkSpace,
@Embedded widget:List<Widget>,
@Embedded feeds:List<Feed>,
)

关系是这样的

workSpaceId|widgetId|feedId|
  1        | 1      | 2
  1        | 1      | 1    |
  2        | 1      | 2
  2        | 2      | 1    

基本上，工作区和小部件以及小部件和提要之间存在多对多关系 当所有三个表都参与时，它们应该聚集在一起

我浏览了指南https://developer.android.com/training/data-storage/room/relationships

并尝试在小部件和工作区以及提要和小部件之间进行两种映射，但是我什至无法使用它构建

我尝试了使用 Workspace 和 Widget 的一对多以及使用 Widget 和 Feed 的多对多，然后我在我的工作区中获得了我不想要的小部件的提要。

在这一点上，我真的很困惑，任何朝着正确方向的轻推将不胜感激

更新

有了下面迈克的回答，我得到了这个

2021-04-04 12:16:06.097 10237-10291/com.example.datacreation D/MainActivty: meta data [IntersectionWithWorkSpaceWidgetFeed(workSpace=WorkSpace(workSpaceId=2, 
associatedUserId=test, workSpaceName=Demo),
 widget=WidgetMetaData(widgetId=11, widgetName=Widget1, backgroundColor=None, widgetType=Normal, dataUrl=www), 
feed=Feed(feedId=2, feedName=Feed2, count=0, asyncInterval=1234)),
 IntersectionWithWorkSpaceWidgetFeed(workSpace=WorkSpace(workSpaceId=2, associatedUserId=test, 
workSpaceName=Demo),
 widget=WidgetMetaData(widgetId=12, widgetName=Widget2, backgroundColor=None, widgetType=normal, dataUrl=www), 
feed=Feed(feedId=1, feedName=Feed1, count=2, asyncInterval=1234)),
 IntersectionWithWorkSpaceWidgetFeed(workSpace=WorkSpace(workSpaceId=2, associatedUserId=igvuser, workSpaceName=Demo),
 widget=WidgetMetaData(widgetId=13, widgetName=Widget3, backgroundColor=None, widgetType=normal, dataUrl=www),
 feed=Feed(feedId=2, feedName=Feed2, count=0, asyncInterval=1234))]

离我原来的 MergedData POJO 足够近了。 谢谢迈克。

Answer 1

我相信你想要一个 3 路映射表。 每行由 3 列组成，WorkSpaceId、WidgetId 和 FeedId，主键由所有 3 列组成。

假设这是一个工作示例：-

3个基本实体：

工作区

@Entity(
    tableName = "workspace_table",
)
data class WorkSpace(
    @PrimaryKey
    val workSpaceId:Long,
    val workPlaceName: String
)

小部件

@Entity(
    tableName = "widget_table",

)
data class Widget(
    @PrimaryKey
    val widgetId:Long,
    val widgetName: String
)

喂养

@Entity(tableName = "feed_table")
data class Feed(
    @PrimaryKey
    val feedId:Long,
    val feedName: String
)

新的映射表WorkSpaceWidgetFeedIntersectionMap

@Entity(
    tableName = "workspace_widget_feed_mapping_table",
    foreignKeys = [
        ForeignKey(
            entity = WorkSpace::class,
            parentColumns = ["workSpaceId"],
            childColumns = ["workSpaceId_map"]
        ),
        ForeignKey(
            entity = Widget::class,
            parentColumns = ["widgetId"],
            childColumns = ["widgetId_map"]
        ),
        ForeignKey(
            entity = Feed::class,
            parentColumns = ["feedId"],
            childColumns = ["feedId_map"]
        )
    ],
    primaryKeys = ["workSpaceId_map","widgetId_map","feedId_map"],
)
data class WorkSpaceWidgetFeedIntersectionMap(

    @NonNull
    val workSpaceId_map: Long,
    @NonNull
    val widgetId_map: Long,
    @NonNull
    val feedId_map: Long
)

• 外键是可选的

道的AllDao

@Dao
interface AllDao {

    @Insert
    fun insertWorkSpace(workSpace: WorkSpace): Long
    @Insert
    fun insertWidget(widget: Widget): Long
    @Insert
    fun insertFeed(feed: Feed): Long
    @Insert
    fun insertWorkSpaceWidgetFeedMap(workSpaceWidgetFeedIntersectionMap: WorkSpaceWidgetFeedIntersectionMap): Long


    @Query("DELETE FROM workspace_table")
    fun clearWorkSpaceTable(): Int
    @Query("DELETE FROM widget_table")
    fun clearWidgetTable(): Int
    @Query("DELETE FROM feed_table")
    fun clearFeedTable(): Int

    @Query("DELETE FROM workspace_widget_feed_mapping_table")
    fun clearWorkSpaceWidgetFeedMap(): Int

    @Query("SELECT * FROM workspace_widget_feed_mapping_table")
    fun getWorkSpaceWidgetFeedIntersections(): List<WorkSpaceWidgetFeedIntersectionMap>

}

数据库MyDatabase

@Database(entities = [WorkSpace::class,Widget::class,Feed::class,WorkSpaceWidgetFeedIntersectionMap::class],version = 1)
abstract class MyDatabase: RoomDatabase() {
    abstract fun getAllDoa(): AllDao
}

最后是一个 Activity MainActivity来测试基本功能

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val db = Room.databaseBuilder(applicationContext,MyDatabase::class.java,"mydb")
            .allowMainThreadQueries()
            .build()
        val dao = db.getAllDoa()
        clearAllTables(dao)
        dao.insertWorkSpace(WorkSpace(1,"WorkSpace 1"))
        dao.insertWorkSpace( WorkSpace(2,"WorkSpace 2"))

        dao.insertWidget(Widget(1,"Widget 1"))
        dao.insertWidget(Widget(2,"Widget 2"))

        dao.insertFeed(Feed(1,"Feed 1"))
        dao.insertFeed( Feed(2,"Feed 2"))

        dao.insertWorkSpaceWidgetFeedMap(WorkSpaceWidgetFeedIntersectionMap(1,1,2))
        dao.insertWorkSpaceWidgetFeedMap(WorkSpaceWidgetFeedIntersectionMap(1,1,1))
        dao.insertWorkSpaceWidgetFeedMap(WorkSpaceWidgetFeedIntersectionMap(2,1,2))
        dao.insertWorkSpaceWidgetFeedMap(WorkSpaceWidgetFeedIntersectionMap(2,2,1))

        val wwfiList = dao.getWorkSpaceWidgetFeedIntersections()
        for(cwwfi: WorkSpaceWidgetFeedIntersectionMap in wwfiList) {
            Log.d("WWFIINFO","WorkSpaceID = " + cwwfi.workSpaceId_map + " WidgetID = " + cwwfi.widgetId_map + " FeedID = " + cwwfi.feedId_map)
        }

    }

    private fun clearAllTables(dao: AllDao) {
        dao.clearWorkSpaceWidgetFeedMap()
        dao.clearFeedTable()
        dao.clearWidgetTable()
        dao.clearWorkSpaceTable()
    }
}

1. 获取构建的数据库（为了方便和简洁，允许在主线程上运行）
2. 得到道
3. 清除所有表（使测试可重新运行）
4. 添加 2 个工作区、2 个小部件和 2 个提要
5. 添加交集 map 条目
6. 提取并记录交叉点

结果

运行上述产生： -

2021-04-04 08:31:02.942 D/WWFIINFO: WorkSpaceID = 1 WidgetID = 1 FeedID = 2
2021-04-04 08:31:02.942 D/WWFIINFO: WorkSpaceID = 1 WidgetID = 1 FeedID = 1
2021-04-04 08:31:02.942 D/WWFIINFO: WorkSpaceID = 2 WidgetID = 1 FeedID = 2
2021-04-04 08:31:02.943 D/WWFIINFO: WorkSpaceID = 2 WidgetID = 2 FeedID = 1

• 然后，您可以轻松地从检索到的 WorkSpaceWidgetFeedIntersectionMap 中获取相应的 WorkSpace、Wdiget 和 Feed。
• 见附加

额外的

现在要获取您的 MergedData （等效），然后考虑对上述内容进行以下添加

1. 新数据 class IntersectionWithWorkSpaceWidgetFeed

:-

class IntersectionWithWorkSpaceWidgetFeed(
    @Embedded
    val workSpace: WorkSpace,
    @Embedded
    val widget: Widget,
    @Embedded
    val feed: Feed
)

2. 一个额外的道 function getWorkSpaceWidgetAndFeedFromIntersectionMap()

:-

@Query("SELECT * FROM workspace_widget_feed_mapping_table JOIN workspace_table ON workSpaceId = workSpaceId_map JOIN widget_table ON widgetId = widgetId_map JOIN feed_table ON feedId = feedId_map")
fun getWorkSpaceWidgetAndFeedFromIntersectionMap(): List<IntersectionWithWorkSpaceWidgetFeed>

3. MainActivity 的 onCreate 方法中的新（或替换现有 6.）部分

:-

    val iwwfList= dao.getWorkSpaceWidgetAndFeedFromIntersectionMap()
    for(iwwf: IntersectionWithWorkSpaceWidgetFeed in iwwfList) {
        Log.d("WWFINFO","WorkSpaceID = " + iwwf.workSpace.workSpaceId + " WorkSpaceName = " + iwwf.workSpace.workPlaceName +
                " WidgetID = " + iwwf.widget.widgetId + " WidgetName = " + iwwf.widget.widgetName +
                " FeedID = " + iwwf.feed.feedId + " FeedName = " + iwwf.feed.feedName
        )
    }

上述变化的结果：-

2021-04-04 09:20:34.371 D/WWFINFO: WorkSpaceID = 1 WorkSpaceName = WorkSpace 1 WidgetID = 1 WidgetName = Widget 1 FeedID = 2 FeedName = Feed 2
2021-04-04 09:20:34.371 D/WWFINFO: WorkSpaceID = 1 WorkSpaceName = WorkSpace 1 WidgetID = 1 WidgetName = Widget 1 FeedID = 1 FeedName = Feed 1
2021-04-04 09:20:34.371 D/WWFINFO: WorkSpaceID = 2 WorkSpaceName = WorkSpace 2 WidgetID = 1 WidgetName = Widget 1 FeedID = 2 FeedName = Feed 2
2021-04-04 09:20:34.371 D/WWFINFO: WorkSpaceID = 2 WorkSpaceName = WorkSpace 2 WidgetID = 2 WidgetName = Widget 2 FeedID = 1 FeedName = Feed 1