many to many relationship to an abstract class?

erikvaningen · **Posted:** Wed Mar 19, 2008 12:59 pm

Code:

public abstract class Building {
   @Id
   Long resourceId;
   
   @ManyToMany(cascade = { CascadeType.ALL })
   private List<Project> projectList;
}

@Entity
public class Office extends Building {}

@Entity
public class House extends Building {}

@Entity
public class Project {
   
   @Id 
   Long id;   
   
   @ManyToMany(cascade = { CascadeType.ALL })
   private List<Building> buildingList;  // here is my problem!!!!!

}

My question is, how do I implement a bidirectional many-to-may relationship between Project and Building? I want to avoid duplicating the relationship from Project to House and from Project to Building. Therefore I want the many to many relation from Project to Building. And I want to create a Project, add an Office to it and save it (entityManager.persist(project)).

I am a dead man by now tried a lot of options, @CollectionOfElements on buildingList ,InheritanceType.SINGLE_TABLE on Building. It all did not work.

Anyone knows which annotations I have to add in order to make this work?

ge0ffrey · **Joined:** Thu Oct 13, 2005 4:19 am **Posts:** 98

put a @Entity and @Inheritance (single table) on Building, write a HQL "... from Building" that proves that that polymorfism works.
Next follow the intructions in the manual on how to map a ManyToMany.

PS: I personally dislike @ManyToMany and always use a relation object (say ProjectBuildingAssigment) with OneToMany's

erikvaningen · **Posted:** Wed Apr 02, 2008 9:08 am

It worked, thanks!

Code:

@Entity
@Inheritance(strategy=InheritanceType.JOINED)
public abstract class ProjectObject extends Resource 

I also had to add InheritanceType.JOINED because there is a bug in Hibernate with PostGres and this solves it.