Does persist always hit the database?

voidmain · **Joined:** Fri Jun 23, 2006 12:52 pm **Posts:** 11

I'm wondering whether or not the JPA EntityManager.persist method is 100% guaranteed to always call the database? Here's a code snippet:

Code:

        EntityManager em = emf.createEntityManager();
        Product p = new Product();
        p.setAmount(1.0);
        p.setName("FooBar");
        EntityTransaction et = em.getTransaction();
        et.begin();
        em.persist(p);

        // Test with JDBC
        Connection c = ((EntityManagerImpl) em).getSession().connection();
        System.out.println("AC = " + c.getAutoCommit());

        Statement s = c.createStatement();
        ResultSet rs = s.executeQuery("select * from products where name = 'FooBar'");
        assertTrue(rs.next());
        assertEquals("FooBar", rs.getString("name"));

So, this works, but my question is will it always work no matter what? Will em.persist always execute the SQL even if there are no GeneratedValues or it is an update?

voidmain · **Joined:** Fri Jun 23, 2006 12:52 pm **Posts:** 11

Okay, so I read closely all the documentation and the answer is a definitive NO. I'll be posting a blog entry about this and I'll be evaluating the other JPA providers to determine which is best. The problem I have with this solution is that Hiberante is trying to be a database instead of a simple ORM. Quite annoying actually.

voidmain · **Joined:** Fri Jun 23, 2006 12:52 pm **Posts:** 11

If I have a MySQL database and the object I'm persisting has a @GeneratedValue annotation anywhere inside it, it HAS to hit the database when I call persist right? Isn't it 100% guaranteed to always have the id set after a call to persist?

emmanuel · **Posted:** Wed Mar 28, 2007 11:37 pm

no this is not guarantied, use save for that

voidmain · **Joined:** Fri Jun 23, 2006 12:52 pm **Posts:** 11

emmanuel wrote:

no this is not guarantied, use save for that

There is no save method via JPA. Were you thinking of something else?

I think I've figured out most of what is happening under the hoods. There are a few conditions that cause this to always write to the database. The easiest of which is to always include a GeneratedValue and always commit within a transaction. This causes the code to assume a flush during every write operation.