@ManyToMany doesn't generate a table with primary key

infinity2heaven · **Posted:** Tue Apr 15, 2008 7:27 pm

Hibernate version:
3.3

Name and version of the database you are using:
Oracle 10g

I have two entities which have a many to many relationship (Foo and Bar).
Using JPA, they are mapped like this: -

Code:

public class Foo {
  ........
@ManyToMany 
@JoinTable(name="foos_bars", joinColumns = { @JoinColumn(name = "foo_id") },
   inverseJoinColumns = { @JoinColumn(name = "bar_id") })
   public List<Bar> getBars() {
      return bars;
   }

Code:

public class Bar {
 .....
@ManyToMany(mappedBy="foos")   
   public List<Foo> getFoos() {
      return foos;
   }
}

I'm using hibernate.hbm2ddl.auto= create-update

The table generated has only two foreign keys (foo_id and bar_id) but no Primary key of it's own. How do I enforce the generation of primary key?
(My DBA insists strict referential integrity for all tables, and I'm using schema generation completely)

infinity2heaven · **Posted:** Mon Apr 21, 2008 1:41 pm

Not a single reply? I'm really concerned about this Issue, atleast would appreciate if anyone has some suggestions.

andydale · **Posted:** Tue Apr 22, 2008 4:55 am

Hi,

I have also found this in the past if you use Lists on both sides of the relationship. I would recommend switching the owning side of the releationship to use a Set, it the generates a table like so:

Code:

CREATE TABLE course_student
(
  course_id int4 NOT NULL,
  student_id int4 NOT NULL,
  CONSTRAINT course_student_pkey PRIMARY KEY (course_id, student_id),
  CONSTRAINT fkee28be175d95483a FOREIGN KEY (course_id)
      REFERENCES course (course_id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION,
  CONSTRAINT fkee28be17d9f37f7a FOREIGN KEY (student_id)
      REFERENCES student (student_id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION
) 

cheers,

Andy

infinity2heaven · **Posted:** Tue Apr 22, 2008 10:28 am

Thanks! That worked with the combined primary key. (Still better than not having any primary key at all)

alanhay · **Joined:** Tue Jul 29, 2008 7:01 am **Posts:** 9

andydale wrote:

I have also found this in the past if you use Lists on both sides of the relationship. I would recommend switching the owning side of the releationship to use a Set, it the generates a table like so:

I have come across this issue as well when using Lists on both sides. When using a Map on one side, the PKs are generated as expected.

Can anyone throw any light on this? Is this as a result of a bug or is there some fundamental reason why this should be the case?

Thanks.

Alan

andydale · **Posted:** Tue Jul 29, 2008 7:18 am

Hi,

I thought this is because you have no guarantee of unique-ness if both sides are Lists (allow duplicate values), however a Set by default does not allow duplicates (same as PKs).

Cheers,

Andy

alanhay · **Joined:** Tue Jul 29, 2008 7:01 am **Posts:** 9

Yeah, managed to figure that one one after a bit of thought. Makes sense.

Thanks for the reply.