JPA：加入和排序 by/limit 约束 child table 的 OneToMany 关系与流利或 @Query

Question

给定以下模型：

@Entity
open class Parent {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    open val id: Long? = null

    @OneToMany(cascade = [CascadeType.ALL])
    @JoinColumn(name = "parent_id")
    @OrderColumn(name = "version")
    private var children: MutableList<Child> = mutableListOf()

    fun addChild(child: Child) {
        child.parent = this
        children.add(child)
    }

    fun getChildPosition(child: Child): Int {
        return children.indexOf(child)
    }
}

@Entity
open class Child {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    open val id: Long? = null

    @ManyToOne
    @JoinColumn(name = "parent_id")
    open var parent: Parent? = null

    @Column(nullable = false)
    open var data: String? = null

    @Column(name = "version")
    open var version: Int? = null

    @PrePersist
    @PreUpdate
    private fun prepareVersion() {
        if (parent != null) {
            version = parent?.getChildPosition(this)
        }
    }
}

interface MyProjection {
  // parent.id, child.id, child.version, child.data 
}

@Repository
interface ParentRepository : JpaRepository<Parent, UUID> {
  @Query("?")
  fun findWithLatestChild(id: Long?): MyProjection?
}

是否可以使用 JPA 方法命名约定或 JPQL 查询来执行以下操作：

在 parent.id 上加入 parent 和 child。
在版本 (desc) 上订购 children 并将结果限制为 1。
投影 properties/columns 如上面的模拟投影界面中所述。

更新：如果这不可行，以下本机查询描述了我的意图：

select p.id,c.* from parent p join child c on p.id = c.parent_id
where p.id = :parentId
order by c.version desc
limit 1

Answer 1

因此您可以创建这样的查询：

@Query("select new packagename.MyProjection(c.parent.id, c.id, c.version, c.data ) " +
       "from Child where c.parent.id = :parentId order by c.version desc")
fun findWithLatestChild(id: Long?, pageable: Pageable): MyProjection?

然后用 PageRequest 调用它以将结果限制为 1

findWithLatestChild(PageRequest.of(0,1));

JPA：加入和排序 by/limit 约束 child table 的 OneToMany 关系与流利或 @Query

JPA: Join and order by/limit constraint on child table of OneToMany relation with fluent or @Query

jpa

spring-data-jpa