hibernate NonUniqueObjectException: a different object with the same identifier value was already associated with the session:

I had this error when opening two sessions. One session for a User and another session for an object that has its primary key a foreign key from User. With this,the two session has the same primary key or identifier. I solved this by session.clear before session.update(type).

public T update(T type) { Session session = getSession(); session.clear(); session.update( type ); session.flush(); return type; }

public String getAccountsDetails(AccountDetails accountDetails) {
        System.out.println("accountDetails.accoundId-->"+accountDetails.getAccountsId());
        Session session = sessionFactory.openSession();
        Query query = session.createQuery("from QBAccounts qba where qba.accountsId=:accId");
        List<AccountDetails> queryList = query.setParameter("accId", accountDetails.getAccountsId()).list();
        session.close();
        Session session2 = sessionFactory.openSession();
//          session.saveOrUpdate(accountDetails);
        try{
            if(queryList.size()>0){                 
                session2.beginTransaction();
                /*
                 *  comment below line-50,51 to use update instead of merge, and uncomment line 53
                 */
                AccountDetails acDet = (AccountDetails) session2.get(AccountDetails.class, new Long(1));//line 50
                session2.merge(accountDetails);//line 51
                System.out.println("acDet-->"+acDet+"  --accountDetails->  "+accountDetails);//line 52
//              session2.update(accountDetails);//line 53
            }else{
                session2.beginTransaction();
                session2.save(accountDetails);
            }
        }catch(DIRException e){
            session2.getTransaction().rollback();
            System.out.println("Getting Exception : " + e.getLocalizedMessage());
        }finally{
             session2.getTransaction().commit();
             session2.close();
        }
        return "Successfully data updated into table";
    }

Removed @GeneratedValue from my dto, since value was coming from UI.

Here is the good article, how to use MERGE/UPDATE

Try using one session only as suggested by lalit.

The code reduced to as below.

private String sessionType=null;
public String getAccountsDetails(List<Account> accountList) {       
    Session session = sessionFactory.openSession();

    for (Account account : accountList) {
        AccountDetails accountDetails = new AccountDetails();
        accountDetails.setAccountsId(Long.parseLong(account.getId()));
        accountDetails.setAccounttype(account.getAccountType().value());
        Query query = session.createQuery("from QBAccounts qba where qba.accountsId=:accId");
        List<AccountDetails> queryList = query.setParameter("accId", accountDetails.getAccountsId()).list();
        if(queryList.size()>0){         
            session.update(accountDetails);
            sessionType = "update";
        }else{
            session.save(accountDetails);
            sessionType = "save";
        }
    }
        session.flush();  
        session.beginTransaction().commit();
        session.clear();
        session.close();


    return "Successfully data updated into table";
}