Under what circumstances are transactions necessary?

mjs · **Joined:** Tue May 04, 2004 11:51 am **Posts:** 8

Under what circumstances are transactions necessary? I have a Customer object with a Map as an instance variable. Modifications to the map are written to the database iff I'm using transactions--is this supposed to happen?

In the following code, the attribute-value pair "COLOUR"/"BLUE" is written to the database iff the tx.commit() line is present--without it, it's not (and not error or Exception is raised).

I'm using Hibernate 2.1 and MySQL 4.0.18.

Code:

   public void testStrange() throws Exception {

      Customer c = new Customer();
      
      Map m = c.getAttribute();

      m.put("COLOUR", "BLUE");

      Session s = dowcarter.Util.getSession();

      s.save(c);

      try {

         Transaction tx = null;

         tx = s.beginTransaction();

         tx.commit();

      }
      catch (Exception e) {
         System.out.println(e);
      }
      
      s.close();

   }

christian · **Posted:** Fri May 07, 2004 12:23 pm

You always have to use transactions to encapsulate/demarcate your units of work, transactions are never ever optional (no, not even for read-only).

christian · **Posted:** Fri May 07, 2004 12:24 pm

Oh, the Hibernate Transaction _API_ is optional! You may manage the JDBC connection (and transaction) yourself, but the Hibernate Transaction API makes it easier to switch to JTA/container managed transactions later.

mjs · **Joined:** Tue May 04, 2004 11:51 am **Posts:** 8

Ah! that would explain it, thanks.

(It it possible to arrange things so that Hibernate does not "work" at all (i.e. doesn't write to database) without transactions? It's kinda perplexing to have your first few un-transactioned Hibernate experiments work fine (un-transactioned for simplicity), but the next few not work at all.)

christian · **Posted:** Tue May 11, 2004 5:04 am

You definitely should get the big picture about transactions first, your description doesn't make much sense. If you don't commit a database transaction (either direct JDBC or the Hibernate API), nothing will be written to the database, as the transaction (remember, there always is one) of the connection is rolled back, as soon as the connection is closed.

mjs · **Joined:** Tue May 04, 2004 11:51 am **Posts:** 8

When using MySQL at least, data is most certainly committed to the database even when transactions are not explicitly used. The following JUnit test writes to the database:

Code:

   public static void testExample() throws Exception {
      Session sess = example.hibernate.Util.getSession();

      Customer c = new Customer();
      
      c.setFirstName("FOO");
      c.setLastName("BAR");
      
      sess.save(c);
      
      sess.close();
   }

christian · **Posted:** Tue May 11, 2004 7:17 am

Because MySQL doesn't support transactions by default! It is not a database.