[FIXED] Changing a OneToMany Bidirectional Relationship to ManyToMany Bidirectional

Issue

I want to convert the following mapping on courseDetails to manyToMany. This is because I get an exception Found shared references to a collection: com.xyz.courseDetails and I assume this happens because the relation is not actually one to many in the database, since there are some course_detail tuples that has multiple courses.

@Entity
@Table(name = "courses")
public class Course
{ 

    @Column(name = "course_detail_id")
    private Long extendedCourseDetailId;
    ...

    @OneToMany(fetch = FetchType.LAZY, targetEntity = CourseDetail.class,  cascade = CascadeType.ALL)
    @JoinColumn(name="id", referencedColumnName="course_detail_id")
    private List<CourseDetail> courseDetails = new ArrayList<>();
}

Simply changing the annotation to ManyToMany does not work, JPA somehow couldn't find the related columns. Why? How can I do this?

Solution

What do you think of this :

• Let's assume the entity CourseDetail has as ID :

public class CourseDetail
{ 
    @Id
    @Column(name = "cd_id")
    private Long courseDetailId;

• So this non tested code might help you.
  • where the table "course__course_detail" will be automatically created to hold the relationship with 2 columns : "course_id" and "coursedetail_id".

@Entity
@Table(name = "courses")
public class Course
{ 
    @Id
    @Column(name = "c_id")
    private Long courseId;

    // @Column(name = "course_detail_id") // I comment because I dont understand the purpose
    // private Long extendedCourseDetailId;
    ...

    
    @ManyToMany(fetch = FetchType.LAZY)
    @JoinTable(name = "course__course_detail", 
        joinColumns = @JoinColumn(name = "course_id", referencedColumnName="c_id"), 
        inverseJoinColumns = @JoinColumn(name = "coursedetail_id", referencedColumnName="cd_id"),
        )
    private List<CourseDetail> courseDetails = new ArrayList<>();
}

PS: NOT TESTED Feel free to tell me more in comments.

Answered By - g.momo
Answer Checked By - Dawn Plyler (JavaFixing Volunteer)