将联结表中的值映射到实体

Question

我有一个USER表和一个COURSE表.用户可以拥有许多课程,而且很多用户都可以参加课程.联结表包含一个ROLE值,用于确定用户在COURSE(即讲师,学生等)中的角色.我需要知道如何将此角色与每个USER的COURSE相关联.

如果我将该角色放在Course类中,它就无法工作,因为一个Course有很多用户,反之亦然.

这是我到目前为止所拥有的:

@Entity
@Table(name = "USERS")
public class User {

@Id
@Column(name = "PK1")
private Long id;

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

@ManyToMany
@JoinTable(name = "COURSE_USERS", 
    joinColumns = @JoinColumn(name = "USERS_PK1", referencedColumnName = "PK1"), 
    inverseJoinColumns = @JoinColumn(name = "CRSMAIN_PK1", referencedColumnName = "PK1"))
private Collection<Course> courses;

...

@Entity
@Table(name = "COURSE")
@SecondaryTable(name = "COURSE_USERS", 
pkJoinColumns = @PrimaryKeyJoinColumn(name = "CRSMAIN_PK1"))
public class Course {

@Id
@Column(name = "PK1")
private Long id;

    // THIS PROBABLY WON'T WORK //
@Column(name = "ROLE", table = "COURSE_USERS")
private Character role;

@Column(name = "AVAILABLE_IND")
private boolean available;

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

@Transient
private String url;

    ...

注意:我无法更改数据库架构,因此联结表是不可协商的.

Answer 1

在你的情况下有第三个实体,它想要出来.你可以称之为CourseAssignment.CourseAssignment将包含角色,以及与用户和角色的ManyToOne关系.此外,当然还有从课程到CourseAssignment以及从User到CourseAssignment的OneToMany关系.

像这样的东西会起作用(我没有尝试过,所以有些东西可能会丢失,但你会明白的.

@Entity
@Table(name = "COURSE_USERS")
@IdClass(CourseAssignmentId.class)
public class CourseAssignment {
    @Id
    @ManyToOne
    @JoinColumn(name="USERS_PK1")
    private User user;
    @Id
    @ManyToOne
    @JoinColumn(name="CRSMAIN_PK1")
    private Course course;

    @Column(name = "ROLE")
    private Character role;
}
//and then of course IdClass, because combined key:
@Embeddable
public class CourseAssignmentId implements Serializable{
    @Column(name="USERS_PK1")
    private Long user;

    @Column(name="CRSMAIN_PK1")
    private Long course;
}


User { ..

    @OneToMany(mappedBy = "user")
    private Collection<CourseAssignment> courseAssignments;
...
}

Course {..
   @OneToMany(mappedBy = "course")
   private Collection<CourseAssignment> course;

..
}

当然,删除那些现有的关系连接属性.