Hibernate many-to-many relationship
- by Capitan
I have two mapped types, related many-to-many.
@Entity
@Table(name = "students")
public class Student{
...
@ManyToMany(fetch = FetchType.EAGER)
@JoinTable(
name = "students2courses",
joinColumns = { @JoinColumn(
name = "student_id",
referencedColumnName = "_id") },
inverseJoinColumns = { @JoinColumn(
name = "course_id",
referencedColumnName = "_id") })
public Set<Course> getCourses() {
return courses;
}
public void setCourses(Set<Course> courses) {
this.courses = courses;
}
...
}
__
@Entity
@Table(name = "courses")
public class Course{
...
@ManyToMany(fetch = FetchType.EAGER, mappedBy = "courses")
public Set<Student> getStudents() {
return students;
}
public void setStudents(Set<Student> students) {
this.students = students;
}
...
}
But if I update/delete Course entity, records are not created/deleted in table students2courses. (with Student entity updating/deleting goes as expected)
I wrote abstract class HibObject
public abstract class HibObject {
public String getRemoveMTMQuery() {
return null;
}
}
which is inherited by Student and Course.
In DAO I added this code (for delete() method):
String query = obj.getRemoveMTMQuery();
if (query != null) {
session.createSQLQuery(query).executeUpdate();
}
and I ovrerided method getRemoveMTMQuery() for Course
@Override
@Transient
public String getRemoveMTMQuery() {
return "delete from students2courses where course_id = " + id + ";";
}
Now it works but I think it's a bad code.
Is there a best way to solve this problem?
