在 Kotlin 房间中插入多对多关系

Question

我正在使用 Android Room 开发一个项目，但我有点坚持使用多对多关系。我发现this 的问题与我的类似，但我仍然无法使用它。

所以我基本上遵循Documentation 并做了一个Reciepe 和成分关系：

@Entity(tableName ="zutaten_table")
data class ZutatenData(
      @PrimaryKey (autoGenerate = true)  val zutatid : Int,
      @ColumnInfo(name = "zutname") var zutname : String,
      //and some more columns
)

@Entity(tableName = "rezepte_table")
data class RezepteData(
    @PrimaryKey (autoGenerate = true)  val rezeptid : Int,
    @ColumnInfo(name = "rezname") var rezname : String,
    @ColumnInfo(name = "bild") var bild:Int
)

@Entity(primaryKeys = ["zutatid", "rezeptid"])
data class RefZutatRezept(
    val zutatid: Int,
    val rezeptid: Int
)

data class ZutatenWithRezept(
    @Embedded val zutat: ZutatenData,
    @Relation(
        parentColumn = "zutatid",
        entity = RezepteData::class,
        entityColumn = "rezeptid",
        associateBy = Junction(value = RefZutatRezept::class,
         parentColumn = "zutatid",
             entityColumn = "rezeptid"
             )
    )
    val rezepte: List<RezepteData>
)
data class  RezeptWithZutat(
    @Embedded val rezept: RezepteData,
    @Relation(
        parentColumn = "rezeptid",
        entityColumn = "zutatid",
        associateBy = Junction(RefZutatRezept::class)
    )
    val zutaten: List<ZutatenData>
)

我对每种数据类型都有一个 Dao（不知道这是正确的方法......）

@Dao
interface  ZutatDao{

    @Query("SELECT * FROM zutaten_table ORDER BY zutname ASC")
    fun getAlphabetizedZutaten(): LiveData<List<ZutatenData>>

    @Insert(onConflict = OnConflictStrategy.IGNORE)
    suspend fun insert(zutname: ZutatenData)

    @Update
    suspend fun update(zutname: ZutatenData)

    @Query("DELETE FROM zutaten_table")
    suspend fun deleteAll()

}

@Dao
interface RezeptDao{

    @Query("SELECT * FROM rezepte_table ORDER BY rezname ASC")
    fun getRezepte() : LiveData<List<RezepteData>>

    @Insert(onConflict = OnConflictStrategy.IGNORE)
    suspend fun insert(rezepte : RezepteData) :Long

    @Query("DELETE FROM rezepte_table")
    suspend fun deleteAll()

}

@Dao
interface ZutatwithRezeptDao{

    @Transaction
    @Query("SELECT * FROM zutaten_table  ORDER BY zutname ASC")
    suspend fun getZutatenWithRezept(): List<ZutatenWithRezept>

    @Insert(onConflict = OnConflictStrategy.IGNORE)
    suspend fun insert(join:RefZutatRezept)
}
@Dao
interface RezeptwithZutatDao {

    @Transaction
    @Query("SELECT * FROM rezepte_table  ORDER BY rezname ASC")
    suspend fun getRezeptwithZutat(): List<RezeptWithZutat>

    @Insert(onConflict = OnConflictStrategy.IGNORE)
    suspend fun insert(join: RefZutatRezept)

}

我现在想插入一个 RezeptWithZutat（我现在正在 populateDatabase 函数中做。）

var ListZutatRez1 = listOf<ZutatenData>( z_kart, z_quark, z_lein)
var rez = RezepteData(0,"Kartoffeln mit Quark", R.drawable.kartoffelnquark)
var rezges =RezeptWithZutat(rez, ListZutatRez1)
rezzut.insert(rezges)

在最后一行我得到错误：“类型不匹配：推断类型是 RezeptWithZutat 但 RefZutatRezept 是预期的”我尝试了一些东西，但它们都给我带来了不同的错误。

所以我的问题是：将 RezeptWithZutat 自动插入到表中是正确的方法（为 RezeptData 和所有确实存在的 ZutatData 条目创建一个条目，并链接 RefZutatRezept 表中的所有内容。）

Answer 1

这不是简单的一行修复。

首先，您需要能够检测 Zutaten 是否存在以及是否存在 Rezepte（因此现有 Rezept 的 RezeptWithZutat 确实会创建一个新的，但会添加到现有的）。

所以前两个新道

• 注意下面的代码没有使用接口，而是使用了抽象类，因此使用了抽象的 fun 来代替 fun。
• 所有的 dao 也被合并到一个抽象类中，即 AllDao。
• 注意我不做 LiveData 的东西，所以代码不使用 LiveData 并且我复制的代码已经删除了所有 LiveData 以便进行工作演示。

:-

@Query("SELECT zutatid FROM zutaten_table WHERE zutname=:zutname")
abstract fun getZutatenIdByName(zutname: String): Int
@Query("SELECT rezeptid FROM rezepte_table WHERE rezname=:rezname")
abstract fun getRezepteIDByName(rezname: String): Int

如果 zutaten/rezept 不存在，这些将返回 id 或 0。

接下来是一个函数，在 AllDao 中（它直接使用 Dao 的），插入 RezeptWithZutat：-

fun insertZutatenWithRezept(rezeptWithZutat: RezeptWithZutat)  {
    var rid = getRezepteIDByName(rezeptWithZutat.rezept.rezname)
    /* find or insert Rezepte according to name */
    if (rid < 1) {
        rid = insert(RezepteData(0,rezeptWithZutat.rezept.rezname,rezeptWithZutat.rezept.bild)).toInt()
    }
    if (rid < 1) {
        /*
            could not find existing Rezepte or insert a new one?????
            should not happen but in case do something here
         */
    } else {
        for (z in rezeptWithZutat.zutaten) {
            var zid = getZutatenIdByName(z.zutname)
            if (zid < 1) {
                zid = insert(ZutatenData(0, z.zutname)).toInt()

            }
            if (zid < 1) {
                /*
                    could not find existing Zutaten or insert new one?????
                    should not happen but in case do something here
                 */
            } else {
                insert(RefZutatRezept(zutatid = zid, rezeptid = rid))
            }
        }
    }
}

• 这不是最有效的方式，因为不存在的 Zutatens 可以一起插入（但代码更复杂），同样 RefZutatRezept 可以一起插入（再次使用更复杂的代码）。

演示（为了方便/简洁，在主线程上运行）

使用上述内容和您的代码/dao（如上更改）然后在 Activity 中：-

    db = TheDatabase.getInstance(this)
    dao = db.getAllDao()

    val r1 = dao.insert(RezepteData(rezeptid = 0,rezname = "REZ1",bild = 1))
    val r2 = dao.insert(RezepteData(rezeptid = 0, rezname = "REZ2", bild = 1))

    val milk = dao.insert(ZutatenData(zutatid = 0,zutname = "Milk"))
    val sugar = dao.insert(ZutatenData(zutatid = 0,zutname = "Sugar"))
    val flour = dao.insert(ZutatenData(zutatid = 0,zutname = "Flour"))
    val eggs = dao.insert(ZutatenData(zutatid = 0,zutname = "Eggs"))

    dao.insert(RefZutatRezept(milk.toInt(),r1.toInt()))
    dao.insert(RefZutatRezept(flour.toInt(),r1.toInt()))
    dao.insert(RefZutatRezept(eggs.toInt(),r1.toInt()))

    Log.d("STAGE1", "data before adding R-With-Z")
    showAllRezeptWithZutatsInDatabase()
    var newRWithZ = RezeptWithZutat(
        RezepteData(0,"REZ3",1),zutaten = listOf(
            ZutatenData(0,"salt"),
            ZutatenData(0,"nutmeg"),
            ZutatenData(0,"cornflour"),
            ZutatenData(0,"corriander"),
            ZutatenData(0,"Milk"), // exists
            ZutatenData(0,"Sugar"), // exists
            ZutatenData(0,"More Sugar")
        )
    )
    dao.insertZutatenWithRezept(newRWithZ)
    Log.d("STAGE2", "data after adding R-With-Z")
    showAllRezeptWithZutatsInDatabase()

    newRWithZ = RezeptWithZutat(
        RezepteData(0,"REZ3",1),
        zutaten = listOf(
            ZutatenData(0,"leek"),
            ZutatenData(0,"apple"),
            ZutatenData(0,"banana"),
            ZutatenData(0,"pineapple"),
            ZutatenData(0,"Milk"), // exists
            ZutatenData(0,"Sugar"),
            ZutatenData(0,"More Sugar")
        ) //Rezepte also exists
    )
    dao.insertZutatenWithRezept(newRWithZ)
    Log.d("STAGE3", "data after adding R-With-Z")
    showAllRezeptWithZutatsInDatabase()
}

fun showAllRezeptWithZutatsInDatabase() {
    for(rzr: RezeptWithZutat in dao.getRezeptwithZutat()) {
        Log.d("DBINFO","Rezept is ${rzr.rezept.rezname} Bild is ${rzr.rezept.bild} ID is ${rzr.rezept.rezeptid}")
        for(z: ZutatenData in rzr.zutaten) {
            Log.d("DBINFO","\tZutaten is ${z.zutname} ID is ${z.zutatid}")
        }
    }
}

当运行（一次）时，日志包括：-

2021-10-25 20:55:47.370 D/STAGE1: data before adding R-With-Z
2021-10-25 20:55:47.377 D/DBINFO: Rezept is REZ1 Bild is 1 ID is 1
2021-10-25 20:55:47.377 D/DBINFO:   Zutaten is Milk ID is 1
2021-10-25 20:55:47.377 D/DBINFO:   Zutaten is Flour ID is 3
2021-10-25 20:55:47.377 D/DBINFO:   Zutaten is Eggs ID is 4
2021-10-25 20:55:47.377 D/DBINFO: Rezept is REZ2 Bild is 1 ID is 2

2021-10-25 20:55:47.425 D/STAGE2: data after adding R-With-Z
2021-10-25 20:55:47.428 D/DBINFO: Rezept is REZ1 Bild is 1 ID is 1
2021-10-25 20:55:47.428 D/DBINFO:   Zutaten is Milk ID is 1
2021-10-25 20:55:47.428 D/DBINFO:   Zutaten is Flour ID is 3
2021-10-25 20:55:47.428 D/DBINFO:   Zutaten is Eggs ID is 4
2021-10-25 20:55:47.428 D/DBINFO: Rezept is REZ2 Bild is 1 ID is 2
2021-10-25 20:55:47.428 D/DBINFO: Rezept is REZ3 Bild is 1 ID is 3
2021-10-25 20:55:47.428 D/DBINFO:   Zutaten is salt ID is 5
2021-10-25 20:55:47.429 D/DBINFO:   Zutaten is nutmeg ID is 6
2021-10-25 20:55:47.429 D/DBINFO:   Zutaten is cornflour ID is 7
2021-10-25 20:55:47.429 D/DBINFO:   Zutaten is corriander ID is 8
2021-10-25 20:55:47.429 D/DBINFO:   Zutaten is Milk ID is 1
2021-10-25 20:55:47.429 D/DBINFO:   Zutaten is Sugar ID is 2
2021-10-25 20:55:47.429 D/DBINFO:   Zutaten is More Sugar ID is 9

2021-10-25 20:55:47.459 D/STAGE3: data after adding R-With-Z
2021-10-25 20:55:47.461 D/DBINFO: Rezept is REZ1 Bild is 1 ID is 1
2021-10-25 20:55:47.461 D/DBINFO:   Zutaten is Milk ID is 1
2021-10-25 20:55:47.461 D/DBINFO:   Zutaten is Flour ID is 3
2021-10-25 20:55:47.461 D/DBINFO:   Zutaten is Eggs ID is 4
2021-10-25 20:55:47.461 D/DBINFO: Rezept is REZ2 Bild is 1 ID is 2
2021-10-25 20:55:47.461 D/DBINFO: Rezept is REZ3 Bild is 1 ID is 3
2021-10-25 20:55:47.462 D/DBINFO:   Zutaten is salt ID is 5
2021-10-25 20:55:47.462 D/DBINFO:   Zutaten is nutmeg ID is 6
2021-10-25 20:55:47.462 D/DBINFO:   Zutaten is cornflour ID is 7
2021-10-25 20:55:47.462 D/DBINFO:   Zutaten is corriander ID is 8
2021-10-25 20:55:47.462 D/DBINFO:   Zutaten is Milk ID is 1
2021-10-25 20:55:47.462 D/DBINFO:   Zutaten is Sugar ID is 2
2021-10-25 20:55:47.462 D/DBINFO:   Zutaten is More Sugar ID is 9
2021-10-25 20:55:47.462 D/DBINFO:   Zutaten is leek ID is 10
2021-10-25 20:55:47.462 D/DBINFO:   Zutaten is apple ID is 11
2021-10-25 20:55:47.462 D/DBINFO:   Zutaten is banana ID is 12
2021-10-25 20:55:47.462 D/DBINFO:   Zutaten is pineapple ID is 13

建议

1. RefZutatRezept 表的 rezeptid 列上的索引。
2. rezname 和 zutname 上的唯一索引（例如，当前您可以使用 id 为 1 的 Milk 和 id 为 2 的 Milk 等）。
3. RefZutatRezept 表上的外键约束以强制参照完整性并级联删除和更新

   1. Cascade 会将父级的相关更改应用于子级。

   2. 例如如果您删除了一个 Zutaten，那么 RefZutatRezept 中所有引用该 Zutaten 的行都会被自动删除

      1. 没有你可能会遇到问题，因为会引用不存在的 Zutaten。对于任何 Rezepte 的

   3. onUpdate 操作并不那么重要，因为您不太可能更改 zutatid 或 rezptid。

所以你不妨考虑以下几点：-

@Entity(
    tableName ="zutaten_table",
    indices = [ Index(value = ["zutname"],unique = true)]
)
data class ZutatenData(
    @PrimaryKey(autoGenerate = true)  val zutatid : Int,
    @ColumnInfo(name = "zutname") var zutname : String
    //and some more columns
) 

和

@Entity(tableName = "rezepte_table",
    indices = [Index(value = ["rezname"],unique = true)]
)
data class RezepteData(
    @PrimaryKey(autoGenerate = true)  val rezeptid : Int,
    @ColumnInfo(name = "rezname") var rezname : String,
    @ColumnInfo(name = "bild") var bild:Int
)

和

@Entity(
    primaryKeys = ["zutatid", "rezeptid"],
    indices = [Index(value = ["rezeptid"])],
    foreignKeys = [
        ForeignKey(
            entity = ZutatenData::class,
            parentColumns = ["zutatid"],
            childColumns = ["zutatid"],
            onDelete = ForeignKey.CASCADE,
            onUpdate = ForeignKey.CASCADE

        ),
        ForeignKey(
            entity = RezepteData::class,
            parentColumns = ["rezeptid"],
            childColumns = ["rezeptid"],
            onDelete = ForeignKey.CASCADE,
            onUpdate = ForeignKey.CASCADE
        )
    ]
)
data class RefZutatRezept(
    val zutatid: Int,
    val rezeptid: Int
)