Can't get Flush to work

jimmyf · **Joined:** Wed Mar 16, 2011 10:54 am **Posts:** 4

Been stuck on this problem a while now.
In short, When I stop the debugger before the last commit is executed am I wrong when I expect the data base to be up to date when I look in it after the flush has been called? If flush does not send all pending updates to the database then what is it for?
The database contains @New@ in the field after the last commit but not after the flush. I have 2 seperate transactions for clarity so I have the field in a known state.

Thanks .... J

Code:

Session session = HibernateUtil.beginTransaction();
      User user1 = (User)session.get(User.class, new Long("7") );   
      user1.setEmailAddress("Old");
      session.getTransaction().commit();
      
      session = HibernateUtil.beginTransaction();
      User user = (User)session.get(User.class, new Long("7") );      
      user.setEmailAddress("New");
      session.flush();
      session.getTransaction().commit();

nordborg · **Posted:** Wed Mar 30, 2011 9:18 am

I guess that depends on which transaction isolation level you are using (in the debug tool). What you are seeing indicates that you are using READ_COMMITTED. If you want to see changes that are not yet committed you should use READ_UNCOMMITTED.

mmerder · **Posted:** Wed Mar 30, 2011 11:03 am

nordborg is right. You are probably checking your database using an SQL-Tool.
Hibernate DOES send the statements to the database when you are calling flush, but if you have a good database it does not make it visible to other transactions as long as your transaction is not committed (transactions are atomic).

jimmyf · **Joined:** Wed Mar 16, 2011 10:54 am **Posts:** 4

Thanks for replies :)
I'm using postgres. Tried getting the transaction level set to READ_UNCOMMITTED but can't get it working ( Task for another day ) but that explains why I don't see the changes with my sql tool until the commit.
However, here is another closely related issue i'm seeing.
Does refresh() do a dirty read from the database? I would have thought it should pull back the last persisted state of my object, and not the state that the last flush() left it in?

Code:

Session session = HibernateUtil.beginTransaction();
      User user1 = (User)session.get(User.class, new Long("7") );   
      user1.setEmailAddress("Old");
      session.getTransaction().commit();
      
      session = HibernateUtil.beginTransaction();
      User user = (User)session.get(User.class, new Long("7") );      
      user.setEmailAddress("New");
      session.flush();

      session.refresh(user);
      //User still has email set to "New",  does this mean that refresh() is doing a "Dirty" read from the database ?
      session.getTransaction().commit();

nordborg · **Posted:** Wed Mar 30, 2011 1:48 pm

Quote:

I'm using postgres.

It seems like Postgres doesn't support READ_UNCOMMITTED. It will accept it but treat it as READ_COMMITTED

http://www.postgresql.org/docs/9.0/stat ... ction.html

Quote:

Does refresh() do a dirty read from the database?

Well, a transaction will always see modifications made in it's own transaction. But this is not a "dirty read" as used in the SQL terminology. Here is a nice document:

http://www.postgresql.org/docs/9.0/stat ... n-iso.html