java - Hibernate : Update many-tomany intermediary table on Delete -

i new hibernate , not understand how should proceed update intermediary table.

i have manytomany relationship between 2 tables : conferences & publications

pojo publication.class :

private list<conference> conferences; ...  @manytomany(targetentity = conference.class, cascade = { cascadetype.persist,       cascadetype.merge })   @jointable(name = "publications_conferences", joincolumns = @joincolumn(name = "publications_id"), inversejoincolumns = @joincolumn(name = "conferences_id"))   public list<conference> getconferences() {     return conferences;   }    public void setconferences(list<conference> conferences) {     this.conferences = conferences;   } 

pojo conference.class :

private list<publication> publications; ... @manytomany(targetentity = publication.class, mappedby = "conferences")   public list<publication> getpublications() {     return publications;   }    public void setpublications(list<publication> publications) {     this.publications = publications;   } 

my table "conferences" contains duplicated records. code check whether 2 conference a,b have similar titles , deletes either or b. now, instead of deleting reference (and therefore record) in intermediary table, update way :

before deleting conference "b":

|publications_id|conferences_id -------------------------------         c       |               d       |       b         

after deleting conference "d":

|publications_id|conferences_id -------------------------------         c       |               d       |              <----- update reference 

i tried following code :

 if (answer == 2) {             deleteconferenceq.setparameter("confid", confidb);              (publication pubb : publicationsb) {                publicationsa.add(pubb);                pubb.getconferences().add(a);               session.save(pubb);             }              int result = deleteconferenceq.executeupdate();             tx.commit();       } 

but receive org.hibernate.hibernateexception: illegal attempt associate collection 2 open sessions. therefore wondering if correct.

edit #1: replaced previous code :

if (answer == 2) {

            iterator<publication> pubbiter = publicationsb.iterator();             while (pubbiter.hasnext()) {               publication pubb = pubbiter.next();               pubbiter.remove();               pubb.getconferences().remove(b);               b.getpublications().remove(pubb);                pubb.getconferences().add(a);               publicationsb.add(pubb);              }             session.save(a);             session.delete(b);           } 

i still have previous exception upon session.save(obj)

can me ? thanks

from jpa/hibernate point of view, shouldn't think join table. need maintain both sides of @manytomany relationship , let hibernate manage database. in case should come down deleting 1 row , adding 1 row join table. code should this

publication pub = ...; conference conftoberemoved = ...; conference conftobeadded = ...;  pub.getconferences().remove(conftoberemoved); // implies equals() , hashcode() implemented conftoberemoved.getpublications().remove(pub); // same here  pub.getconferences().add(conftobeadded); conftobeadded.getpublications().add(pub);  // save