From: Ellen Kraffmiller <ekraffmiller_at_hmdc.harvard.edu>
Date: Wed, 16 Aug 2006 16:46:13 -0400

Hi,
I have defined two Entities with a ManyToMany relationship along the
following lines:

@Entity
public class VDC {
    @Id private Long id;
    @ManyToMany
      @JoinTable(name="VDC_ADV_SEARCH_FIELDS",
           joinColumns=_at_JoinColumn(name="vdc_id"),
           inverseJoinColumns=_at_JoinColumn(name="study_field_id"))
      private Collection<StudyField> advSearchFields;
      ...
   }

@Entity
public class StudyField {
   @Id private Long id;
   @ManyToMany(mappedBy="advSearchFields")
   private Collection<VDC> advSearchFieldVDCs;
   ...
}

When generate a db schema from these entities, the following
relationship table is created:

CREATE TABLE vdc_adv_search_fields
(
 vdc_id int8 NOT NULL,
 study_field_id int8,
 CONSTRAINT vdc_adv_search_fields_pkey PRIMARY KEY (vdc_id),
 CONSTRAINT fk_vdc_adv_search_fields_study_field_id FOREIGN KEY
(study_field_id)
     REFERENCES studyfield (id) MATCH SIMPLE
     ON UPDATE NO ACTION ON DELETE NO ACTION,
 CONSTRAINT fk_vdc_adv_search_fields_vdc_id FOREIGN KEY (vdc_id)
     REFERENCES vdc (id) MATCH SIMPLE
     ON UPDATE NO ACTION ON DELETE NO ACTION
)
WITHOUT OIDS;
ALTER TABLE vdc_adv_search_fields OWNER TO "vdcApp";

My question is, why is the primary key defined only on vdc_id? I
believe the primary key should be composed of vdc_id and study_field_id.
Is there something I need to change on my mapping?

I am running on Glassfish (Sun App Server 9.0 build b06) and using
PostrgeSQL database.

Thanks
Ellen