JPA EntityTransaction, creating and persisting a new object

Question

I have some confusion with some simple examples i am looking at for Eclipselink and persisting objects. Very new to this. Does it matter at what point you create and mutate an object to save in a database? eg Does all of the work you do with the object have to be done AFTER em.getTransaction().begin(); is called? or can you do what ever you need with that object and then begin, persist, close?

I am using this example with Tomcat. non-jta RESOURCE_LOCAL

The differences in question below:

    EntityManagerFactory factory = Persistence.createEntityManagerFactory(PERSISTENCE_UNIT_NAME);
    EntityManager em = factory.createEntityManager();

 // Creating and mutating object BEFORE begin() is called
    Todo todo = new Todo();
    todo.setSummary("sum");
    todo.setDescription("desc");

    // create new todo
    em.getTransaction().begin();
    em.persist(todo);
    em.getTransaction().commit();

Vs

EntityManagerFactory factory = Persistence.createEntityManagerFactory(PERSISTENCE_UNIT_NAME);
EntityManager em = factory.createEntityManager();


em.getTransaction().begin();

// Creating and mutating object AFTER begin() is called
Todo todo = new Todo();
todo.setSummary("sum");
todo.setDescription("desc");

em.persist(todo);
em.getTransaction().commit();

Answer 1

There is no difference, when you create you object. after begin or before begin.

Answer 2

In fact there is no difference. Because transaction deals only with saving in the database of the persisted entity (entity is a java object: todo in your case). The last thing you do with you entity is flushing it in database (with commit() )