kotlin android 房间外键

Question

我有两个实体 A 和 B，其中一行是 id ，接下来我有实体 Test 它看起来像：

@Parcelize
@Entity(
    tableName = "social_group_discount_relations", primaryKeys = ["oneID", "twoId"],
    foreignKeys = [
        ForeignKey(
            entity = A::class,
            parentColumns = ["id"],
            childColumns = ["oneID"],
            onDelete = CASCADE
        ), ForeignKey(
            entity = B::class,
            parentColumns = ["id"],
            childColumns = ["twoId"],
            onDelete = CASCADE
        )
    ]
)
data class Test(
    @SerializedName("oneID") val oneID: Long,
    @SerializedName("twoId") val twoId: Long
) : Parcelable

接下来我想试试 get 和 obcject ：

日期类 AB (@Embedded val a: A, @Embedded val b: B)@Parcelize @实体（ tableName = "折扣" )

data class Discount(
    @PrimaryKey @SerializedName("id") val id: Long,
    @SerializedName("description") val description: String?,
    @SerializedName("name") val name: String?,
    @SerializedName("rate") val rate: Int?,
    @SerializedName("operator") val operatorId: Long?

) : Parcelable

@Parcelize
@Entity(tableName = "social_group_discount")
data class SocialGroupDiscount(
    @PrimaryKey @SerializedName("id") val id: Long,
    @SerializedName("description") val description: String?,
    @SerializedName("name") val name: String?,
    @SerializedName("code") val code: String?,
    @SerializedName("operator") val operator: Long?

) : Parcelable

@Parcelize
data class SocialGroupAndDiscount(
    @Embedded(prefix = "first_") val discount: Discount,
    @Embedded(prefix = "second_") val socialGroupDiscountRelations: SocialGroupDiscountRelations

) : Parcelable


@Parcelize
@Entity(
    tableName = "social_group_discount_relations", primaryKeys = ["socialGroupId", "discountId"],
    indices = [
        Index(value = ["socialGroupId"]),
        Index(value = ["discountId"])
    ],
    foreignKeys = [
        ForeignKey(
            entity = Discount::class,
            parentColumns = ["id"],
            childColumns = ["discountId"],
            onDelete = CASCADE
        ), ForeignKey(
            entity = SocialGroupDiscount::class,
            parentColumns = ["id"],
            childColumns = ["socialGroupId"],
            onDelete = CASCADE
        )
    ]
)
open class SocialGroupDiscountRelations(
    @SerializedName("socialgroupid") val socialGroupId: Long,
    @SerializedName("discountid") val discountId: Long
) : Parcelable

这是我的查询：

@Query(
        "SELECT discount.id as first_id,discount.name as first_name, discount.rate as first_rate, discount.operatorId as first_operator, discount.description as first_description " +
                " social_group_discount.id as second_id, social_group_discount.name as second_name, social_group_discount.code as second_code, social_group_discount.description as second_description," +
                "social_group_discount.operator as second_operator FROM social_group_discount_relations as AB" +
                " INNER JOIN discount on discount.id=AB.discountId INNER JOIN social_group_discount on social_group_discount.id=AB.socialgroupid"
    )
    fun getAB(): List<SocialGroupAndDiscount>

我在三等舱有一个班级折扣和 socialGroupDiscount，我得到了 List ids discountId 和 groupId，接下来我想创建将这个 ids 映射到折扣和团体折扣的对象

Answer 1

您可以尝试查找many-to-many relationships，但我不确定您是否可以仅使用 Room 工具获得所需的内容。

相反，您可以对 sqlite-query 使用不那么干净的决策：

1. 在嵌入对象的字段中使用前缀以确保结果表中的字段不会混合：

   data class AB (@Embedded(prefix = "first_") val a: A, @Embedded(prefix = "second_") val b: B )

2. 在您的 DAO 中，对所有需要的表进行“手动”查询，但在这种情况下，您必须获取实体 A 和 B 的所有字段并为它们添加前缀：

   @Query(" SELECT A.id as first_id,A.someField as first_someField, B.id as second_id, B.anotherField as second_anotherField FROM social_group_discount_relations as AB INNER JOIN A on A.id=AB.oneID INNER JOIN B on B.id=AB.twoId ") fun getAB(): List<AB>

更新示例

假设您有带字段的 A 类：

• 身份证
• 姓名

还有你的 B 类结构：

• 身份证
• 地址
• 数量

那么你的数据类 AB 应该是：

data class AB (@Embedded(prefix = "first_") val a: A,
  @Embedded(prefix = "second_") val b: B
)

还有你的 DAO 方法：

@Query("SELECT A.id as first_id,A.name as first_name, 
B.id as second_id, B.address as second_address, B.quantity as second_quantity 
FROM social_group_discount_relations as AB 
INNER JOIN A on A.id=AB.oneID 
INNER JOIN B on B.id=AB.twoId")
fun getAB(): List<AB>