How Do I Create Many to Many Hibernate Mapping for Additional Property from the Join Table?
hibernate, hibernate-mapping, spring
Solution
You need to use `@EmbeddedId` and `@Embeddable` annotations to solve this issue:
Lecturer Class:
@Entity
@Table(name="LECTURER")
public class Lecturer {
@OneToMany(fetch = FetchType.LAZY, mappedBy = "pk.lecturer", cascade=CascadeType.ALL)
Set<LecturerCourse> lecturerCourses == new HashSet<LecturerCourse>();
//all others properties Setters and getters are less relevant.
}
Course class:
@Entity
@Table(name="COURSE")
public class Course {
@OneToMany(fetch = FetchType.LAZY, mappedBy = "pk.course", cascade=CascadeType.ALL)
Set<LecturerCourse> lecturerCourses == new HashSet<LecturerCourse>();
//all others properties Setters and getters are less relevant.
}
LecturerCourse Class:
@Entity
@Table(name = "lecturer_course")
@AssociationOverrides({
@AssociationOverride(name = "pk.lecturer",
joinColumns = @JoinColumn(name = "LECTURER_ID")),
@AssociationOverride(name = "pk.course",
joinColumns = @JoinColumn(name = "COURSE_ID")) })
public class LecturerCourse {
private LecturerCourseID pk = new LecturerCourseID();
@Column(name = "CAPACITY", nullable = false, length = 10)
private String capacity;
@EmbeddedId
public LecturerCourseID getPk() {
return pk;
}
}
Now the Primary Key:
@Embeddable
public class LecturerCourseID implements java.io.Serializable {
private Lecturer lecturer;
private Course course;
@ManyToOne
public Stock getLecturer() {
return lecturer;
}
public void setLecturer(Lecturer lecturer) {
this.lecturer= lecturer;
}
@ManyToOne
public Course getCourse() {
return course;
}
public void setCourse(Course course) {
this.course= course;
}
}
now Your Main should be something like this:
Lecturer lecturer1 = new Lecturer();
Course math = new Course();
LecturerCourse lecturer1math = new LecturerCourse();
lecturer1math.setCapacity("capacity");
lecturer1math.setLecturer(lecturer1);
lecturer1math.setCourse(math);
lecturer1.getLecturerCourses().add(lecturer1math);
//saving object
session.save(lecturer1);
You need to be sure that class marked as `@Embeddable` should implement `Serializable` marker interface.
Hope it helps.
Problem
I need a many to many hibernate mapping needed 3 joins. I've tried to find out a solution without intermediate entity like `LecturerCourse`. I have a many to many relation in my database between my lecturer and course tables. A course can be given by several lecturer while a lecturer can give several courses. I have courses stored before hand. However, I need to assign courses to lecturer. When I assign courses I also store the capacity of that course. My database diagram: I use hibernate and spring. I need a hibernate mapping when a course is assign any lecturer. I need to add values to capacity field. My lecturer mapping : ``` @Entity @Table(name="LECTURER") public class Lecturer { @Id @GeneratedValue(strategy=GenerationType.SEQUENCE, generator="LECTURER_ID_SEQ") @SequenceGenerator(name="LECTURER_ID_SEQ", sequenceName="LECTURER_ID_SEQ") private Long Id; @Column(name="NAME") private String name; @Column(name="SURNAME") private String surname; @Column(name="EMAIL") private String email; @Column(name="USERNAME") private String username; @Column(name="PASSWORD") private String Password; @ManyToMany @JoinTable( name="LECTURER_COURSE", joinColumns=@JoinColumn(name="LECTURER_ID"), inverseJoinColumns=@JoinColumn(name="COURSE_ID") ) private List<Course> courses; //getters - setters } ``` My course mapping : ``` @Entity @Table(name="COURSE") public class Course { @Id @GeneratedValue(strategy=GenerationType.SEQUENCE, generator="COURSE_ID_SEQ") @SequenceGenerator(name="COURSE_ID_SEQ", sequenceName="COURSE_ID_SEQ") private Long id; @Column(name="NAME") private String name; @Column(name="CODE") private String code; } ``` Any idea how to solve my problem ?