问题描述

我似乎在网上找不到任何关于在 Spring JDBC 中使用多对一映射的参考资料.我刚刚在不支持的文档中看到了，但我不确定是否是这种情况.

I can't seem to find any reference online with regards to using a Many-To-One mapping in Spring JDBC. I just saw in the documentation that is not supported but I'm not sure if this is the case.

我的示例是我想将我的 AppUser 映射到特定部门.

My example is that I want to map my AppUser to a particular Department.

作为参考，AppUser 使用 DEPARTMENT_ID 加入 Department 表

For reference, AppUser joins to Department table using DEPARTMENT_ID

@Table(value="m_appuser")
public class AppUserProjectionTwo {
    @Id
    private Long id;
    private String firstname;
    private String middlename;
    private String lastname;



    @Column("DEPARTMENT_ID")
    private DepartmentProjection departmenProjection;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

但是，它似乎无法正确映射.

However, it seems that it won't map properly.

@Table("M_DEPARTMENT")
public class DepartmentProjection {
    @Id
    private Long id;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

创建的查询如下所示.我正在寻找更多相反的东西，其中 M_APPUSER.department_ID = Department.id

The created query looks like this. I was looking for something more of the opposite in which M_APPUSER.department_ID = Department.id

[SELECT "m_appuser"."ID" AS "ID", "m_appuser"."LASTNAME" AS "LASTNAME", "m_appuser"."FIRSTNAME" AS "FIRSTNAME", "m_appuser"."MIDDLENAME" AS "MIDDLENAME", "departmenProjection"."ID" AS "DEPARTMENPROJECTION_ID" FROM "m_appuser" LEFT OUTER JOIN "M_DEPARTMENT" AS "departmenProjection" ON "departmenProjection"."DEPARTMENT_ID" = "m_appuser"."ID" WHERE "m_appuser"."FIRSTNAME" = ?];

谢谢

推荐答案

我刚刚在文档中看到不支持，但我不确定是否是这种情况.

I just saw in the documentation that is not supported but I'm not sure if this is the case.

我可以确认它不受支持.多对一关系跨越聚合的边界.跨聚合的引用必须建模为被引用聚合的 id.

I can confirm it is not supported. Many-To-One relationships cross the boundaries of aggregates. References across aggregates must be modelled as ids of the referenced aggregate.

如果你不这样做，Spring Data JDBC 将把引用视为一对一关系和同一聚合的一部分，这将对多对一关系产生你不想要的影响，例如当被引用的实体被删除时，被引用的实体被删除.这对于同一聚合中的一对一关系是正确的.

If you don't do this Spring Data JDBC will consider the reference a One-To-One relationship and part of the same aggregate which will have effects you don't want for a Many-To-One relationship, like the referenced entity getting deleted when the referenced entity gets deleted. Which would be correct for a One-To-One relationship within the same aggregate.

这在 中有更详细的解释https://spring.io/blog/2018/09/24/spring-data-jdbc-references-and-aggregates

这篇关于Spring Data JDBC - 多对一关系的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持跟版网！