Question

从图片中，是否可以将QUALIFICATION_ID作为ID的外键而无需额外的映射列或表？

TABLE - ＆gt; TM_QUALIFICATIONS 是主表，ID是自动生成的UUID，名称是String值。应用程序启动时，值将插入此表中。

TABLE - ＆gt; TM_USER_QUALIFICATIONS ，一个用户可以拥有多种资格。

因此，如果没有任何其他额外的映射列或表，是否可以将QUALIFICATION_ID标记为外键？

另外，我如何组合USER_ID和QUALIFICATION_ID来为TM_USER_QUALIFICATIONS表制作复合主键？

提前致谢

Answer 1

如果没有额外的列或额外的映射表，我认为你不能定义外键关系。

如果我理解正确你可以做点什么

<强> TM_QUALIFICATIONS

    @Entity
    @Table(name = "TM_QUALIFICATIONS")
    public class Qualifications {

        @Id
        @GeneratedValue(generator = "uuid")
        @GenericGenerator(name = "uuid", strategy = "uuid2")
        @Column(name = "ID")
        private String id;

        @Column(name = "NAME")
        private String name;

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

    }

并将QUALIFICATION_ID作为外键，你可以编写单独的DDL来添加约束。

@Repository
public interface UserQualificationsRepository extends CrudRepository<UserQualifications, String>{

    @Modifying
    @Transactional
    @Query(value = "ALTER TABLE TM_USER_QUALIFICATIONS ADD FOREIGN KEY (QUALIFICATION_ID) REFERENCES TM_QUALIFICATIONS(ID)", nativeQuery = true)
    public void addForeignKeyConstraint();
}

<强> TM_USER_QUALIFICATIONS

@Entity
@Table(name = "TM_USER_QUALIFICATIONS")
@IdClass(UserQualificationPK.class)
public class UserQualifications {

    @Id
    @Column(name = "USER_ID")
    private String userId;

    @Column(name = "LEVEL")
    private int level = 0;

    @Id
    @Column(name = "QUALIFICATION_ID")
    private String qualificationId;

    public String getUserId() {
        return userId;
    }

    public void setUserId(String userId) {
        this.userId = userId;
    }

    public int getLevel() {
        return level;
    }

    public void setLevel(int level) {
        this.level = level;
    }
}

最后，对于复合主键，使用@IdClass注释

public class UserQualificationPK implements Serializable {

    private String userId;

    private String qualificationId;

    public UserQualificationPK(String userId, String qualificationId) {
        this.userId = userId;
        this.qualificationId = qualificationId;
    }

    public String getUserId() {
        return userId;
    }

    public void setUserId(String userId) {
        this.userId = userId;
    }

    public String getQualificationId() {
        return qualificationId;
    }

    public void setQualificationId(String qualificationId) {
        this.qualificationId = qualificationId;
    }
}

通过这种方式，你可以达到你的要求。 TM_QUALIFICATIONS和TM_USER_QUALIFICATIONS之间没有关系，但是您通过本机SQL将QUALIFICATION_ID明确定义为外键。

JAP如何在没有额外列或额外映射表的情况下拥有主键外键关系

1 个答案: