处理 Room 数据库中的嵌套实体

Question

我想将这些实体插入数据库： 看来我无法正确构建嵌套实体。我需要你的帮助

[1] 文章实体

@Entity(
tableName = "articles",
foreignKeys = [
    ForeignKey(
        entity = PartCargo::class,
        parentColumns = ["tId"],
        childColumns = ["partTId"],
        onDelete = ForeignKey.CASCADE
        )
   ]
)
data class ArticleEntity(
    @PrimaryKey(autoGenerate = true)
    val tId: Long = 0,
    val partTId: Long = -1,
    val id: String?,
    val name: String?,
) : Serializable

[2] 部分实体

@Entity(
tableName = "parts",
foreignKeys = [
    ForeignKey(
        entity = DetailsCargo::class,
        parentColumns = ["tId"],
        childColumns = ["detailsTId"],
        onDelete = ForeignKey.CASCADE
     )
   ]
)
data class PartCargo(
    @PrimaryKey(autoGenerate = true)
    val tId: Long = 0,
    val detailsTId: Long = -1,
    val id: String?,
    val name: String?,
) : Serializable

data class PartEntity(
    @Embedded
    val part: PartCargo,

    @Relation(parentColumn = "tId", entityColumn = "partTId")
    val partArticles: List<ArticleEntity>?
) : Serializable

[3] 详情实体

@Entity(tableName = "details")
data class DetailsCargo(
    @PrimaryKey(autoGenerate = true)
    val tId: Long = 0,
    val id: String?,
    val name: String?
) : Serializable

data class DetailsEntity(
    @Embedded
    val details: DetailsCargo,

    @Relation(parentColumn = "tId", entityColumn = "detailsTId")
    val parts: List<PartEntity>?

) : Serializable

---

这是详情DAO

@Dao
interface DetailsDAO {

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    fun insertPartCargo(parent: PartCargo): Long

    @Transaction
    fun insertAllParts(parentId: Long, parts: List<PartEntity>) {
        parts.forEach { part ->
            val cargoParentId = insertPartCargo(part.part.copy(detailsTId = parentId))
            part.partArticles?.let { items ->
                val children = items.map { it.copy(partTId = cargoParentId) }
                insertArticleEntities(children)
            }
        }
    }


    @Insert(onConflict = OnConflictStrategy.REPLACE)
    fun insertDetailsCargo(parent: DetailsCargo): Long

    @Transaction
    fun insertDetails(details: DetailsEntity) {
        val parentId = insertDetailsCargo(details.details)

        details.parts?.let { items ->
            insertAllParts(parentId, items)
        }
    }

    @Transaction
    @Query("SELECT * FROM details WHERE :id = id")
    fun getDetails(id: String): DetailsEntity?
}

---

现在，我在构建应用程序时遇到此错误：

Cannot find the child entity column `detailsTId` in PartEntity.

---

• 我的实体构建正确吗？
• 如果不行，有什么解决办法吗？

提前致谢

Answer 1

未完全检查关系，但如果您使用分层（嵌套），则较低的

@Relation

注释应反映实体（列所在的表）而不是 POJO。

@Relation

有一个实体参数，应该使用它，因此我相信您的问题可以通过使用来解决：-

data class DetailsEntity(
    @Embedded
    val details: DetailsCargo,
    @Relation(entity = PartCargo::class, parentColumn = "tId", entityColumn = "detailsTId")
    val parts: List<PartEntity>?

) : Serializable

• 注意定义 PartCargo 类的实体，否则字段的类型用于确定用于构建结果的列
• 您可能希望考虑始终对实体参数进行编码。

没有（注释掉）则：-

与：-

您可能希望留意 3 条警告并在相应字段上使用

@ColumnInfo

，例如

....
@ColumnInfo(index = true)
val partTId: Long = -1,
....