問題描述

我似乎在網上找不到任何關于在 Spring JDBC 中使用多對一映射的參考資料.我剛剛在不支持的文檔中看到了，但我不確定是否是這種情況.

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.

我的示例是我想將我的 AppUser 映射到特定部門.

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

作為參考，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，它似乎無法正確映射.

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;
    }

創建的查詢如下所示.我正在尋找更多相反的東西，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" = ?];

謝謝

推薦答案

我剛剛在文檔中看到不支持，但我不確定是否是這種情況.

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

我可以確認它不受支持.多對一關系跨越聚合的邊界.跨聚合的引用必須建模為被引用聚合的 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.

如果你不這樣做，Spring Data JDBC 將把引用視為一對一關系和同一聚合的一部分，這將對多對一關系產生你不想要的影響，例如當被引用的實體被刪除時，被引用的實體被刪除.這對于同一聚合中的一對一關系是正確的.

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.

這在 中有更詳細的解釋https://spring.io/blog/2018/09/24/spring-data-jdbc-references-and-aggregates

這篇關于Spring Data JDBC - 多對一關系的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！