Something is wrong with my transactions

manugarciac · **Joined:** Fri Nov 21, 2008 8:56 pm **Posts:** 15

I'm doing something really simple with my BD, and it appears to be failing. The code is below. Basically, what myMethod() does is check if certain entry on my DB matches a certain criteria, and if it doesn't, it inserts an object that matches it.
Well, I've detected that when in my application two threads go trough that point at once, it sometimes saves the object twice. Am I doing something wrong with the transaction?

Code:

public void myMethod() {
   try{
      sessionFactory.getCurrentSession().beginTransaction();

      MyObject myObject = getSomeObjectFromDB("1234");
      if (myObject == null) {
         myObject = new MyObject();
         myObject.setSomeParam("1234");
   
         sessionFactory.getCurrentSession().saveOrUpdate(myObject);
      }

      sessionFactory.getCurrentSession().getTransaction().commit();

   } catch (Throwable d) {
      sessionFactory.getCurrentSession().getTransaction().rollback();
   }
}


public MyObject getSomeObjectFromDB(String param){
   Criteria criteria = sessionFactory.getCurrentSession().createCriteria(MyObject.class);
   criteria.add(Expression.eq("someParam", param));
   return criteria.list().isEmpty() ? null : (MyObject)criteria.list().get(0);
}

mmerder · **Posted:** Wed Nov 25, 2009 9:32 am

Thats just a thread concurrency problem. One thread could execute the query being interrupted after getting the result. Now the other threads does the query also getting no result. So both threads will execute the persist. The easiest thing of hadling this issue is making the whole method synchronized.

manugarciac · **Joined:** Fri Nov 21, 2008 8:56 pm **Posts:** 15

Yeah, I came to that conclusion after posting. I thought that transactions blocked...