具有相同名称的键的 Kotmin Room crossRef 实体

Question

我正在创建一个 CRUD 工厂。基本上，我所有的实体都将从以 id 作为主键的 BaseEntity 继承我试图了解如何为 M2M 关系创建交叉引用 table。这是一个没有继承的简化示例。 ArticlesEntity 有很多 MagasinsEntity 和 MagasinsEntity 很多 ArticlesEntity。实体 ArticlesMagasinsCrossRef 是结点

但是 ArticlesEntity 和 MagasinsEntity 都有 id 作为主键。

@Entity(
    tableName = "articles"
)
data class ArticlesEntity(
    @PrimaryKey(autoGenerate = false) val id: UUID = UUID.randomUUID(),
    val title: String,
)

@Entity(tableName = "magasins")
data class MagasinsEntity(
    @PrimaryKey(autoGenerate = false) val id: UUID = UUID.randomUUID(),
    val nomMagasin: String

)

@Entity(
    tableName = "articles_magasins"
   )

data class ArticlesMagasinsCrossRefEntity(
    val id: UUID, // how is it possible here to have the id of Articles ?
    val id: UUID // how is it possible here to have the id of Magasins ?
)

编辑我当然尝试更改列的名称：

data class ArticlesMagasinsCrossRefEntity(
            val articleRd: UUID
            val magasinId: UUID 
        )

但是关系数据构建失败class：例如

data class RelMagasinWithArticles(

    @Embedded val magasin: MagasinsEntity,
    @Relation(
        parentColumn = "magasinId",
        entityColumn = "id",
        associateBy = Junction(ArticlesMagasinsCrossRefEntity::class)
    )
    val articles: List<ArticleEntity>

)

Answer 1

您需要使用 Junction 的 parentColumn 和 entityColumn 参数，例如

data class RelMagasinWithArticles(

    @Embedded val magasin: MagasinsEntity,
    @Relation(
        parentColumn = "id", /* The column in the @Embedded table (articles) */
        entityColumn = "id", /* The column in the Related table (magasins) */
        associateBy = Junction(
            ArticlesMagasinsCrossRefEntity::class,
            parentColumn = "magasinId", /* The column in the junction table that maps to the @Embedded table */
            entityColumn = "articleRd" /* The column in the junction table that maps to the @Relation Table */
        )
    )
    val articles: List<ArticlesEntity>
)

备注

您还需要为 ArticlesMagasinsCrossRefEntity class 定义一个主键，例如:-

@Entity(
    tableName = "articles_magasins",
    /*<<<<< all Room table MUST have a primary key */
    /* as primary key on a single column would be restrictive use a composite
        primary key
     */
    primaryKeys = ["articleRd","magasinId"] 
)

data class ArticlesMagasinsCrossRefEntity(

    /* Cannot have identical member names - i.e. only 1 could be id
    val id: UUID, // how is it possible here to have the id of Articles ?
    val id: UUID // how is it possible here to have the id of Magasins ?
     */
    val articleRd: UUID,
    /* Room will issue warning if the is no index on the 2nd column */
    @ColumnInfo(index = true)
    val magasinId: UUID
)

请注意，您可以使用@ColumnInfo 名称参数来指定列名称。

演示

所以使用你的代码，建议的代码覆盖你的代码，并使用以下@Dao 接口：-

@Dao
interface AllDao {

    @Insert
    fun insert(articlesEntity: ArticlesEntity)
    @Insert
    fun insert(magasinsEntity: MagasinsEntity)
    @Insert
    fun insert(articlesMagasinsCrossRefEntity: ArticlesMagasinsCrossRefEntity)

    @Query("SELECT * FROM magasins")
    @Transaction
    fun getMWA(): List<RelMagasinWithArticles>
}

一个合适的@Database注解class和代码在activity:-

lateinit var db: TheDatabase
lateinit var dao: AllDao
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)
    db = TheDatabase.getInstance(this)
    dao = db.getAllDao()

    val a1uuid = UUID.randomUUID()
    val a2uuid = UUID.randomUUID()
    val a3uuid = UUID.randomUUID()
    dao.insert(ArticlesEntity(a1uuid, "Article1"))
    dao.insert(ArticlesEntity(a2uuid,"Article2"))
    dao.insert(ArticlesEntity(a3uuid,"Article3"))

    val m1uuid = UUID.randomUUID()
    val m2uuid = UUID.randomUUID()
    val m3uuid = UUID.randomUUID()
    dao.insert(MagasinsEntity(m1uuid,"Magasin1"))
    dao.insert(MagasinsEntity(m2uuid,"Magasin2"))
    dao.insert(MagasinsEntity(m3uuid,"Magasin3"))

    dao.insert(ArticlesMagasinsCrossRefEntity(a1uuid,m2uuid))
    dao.insert(ArticlesMagasinsCrossRefEntity(a1uuid,m3uuid))

    dao.insert(ArticlesMagasinsCrossRefEntity(a2uuid,m1uuid))

    dao.insert(ArticlesMagasinsCrossRefEntity(a3uuid,m1uuid))
    dao.insert(ArticlesMagasinsCrossRefEntity(a3uuid,m2uuid))
    dao.insert(ArticlesMagasinsCrossRefEntity(a3uuid,m3uuid))

    val sb = StringBuilder()
    for(mwa in dao.getMWA()) {
        sb.append("\nMagasin is ${mwa.magasin.nomMagasin}. ID is ${mwa.magasin.id} it has ${mwa.articles.size} articles. They are:-" )
        for (article in mwa.articles) {
            sb.append("\n\tArticle is ${article.title} ID is ${article.id}")
        }
    }
    Log.d("DBINFO",sb.toString())
}

日志的输出是：-

D/DBINFO: Magasin is Magasin1. ID is 0f3384ee-6232-423e-b2f1-a12ebdac6487 it has 2 articles. They are:-
        Article is Article2 ID is 2729d017-de05-41d2-8de3-8351dfca0a6b
        Article is Article3 ID is 42057ea7-bc03-409f-b2b8-2dc3fa5def19
    Magasin is Magasin2. ID is ba649833-a8ce-4cf2-a1b8-bcab8f7a7d0a it has 2 articles. They are:-
        Article is Article1 ID is 8763421d-b86d-4725-8e6b-65570958ebdc
        Article is Article3 ID is 42057ea7-bc03-409f-b2b8-2dc3fa5def19
    Magasin is Magasin3. ID is eed6f0a5-0825-4cda-9eb4-c4e973a49738 it has 2 articles. They are:-
        Article is Article1 ID is 8763421d-b86d-4725-8e6b-65570958ebdc
        Article is Article3 ID is 42057ea7-bc03-409f-b2b8-2dc3fa5def19

具有相同名称的键的 Kotmin Room crossRef 实体

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