@Entity
public class Foo {

    @Id
    private Long id;

    private String name;

    // <init>s and getters and setters


public class EntityTests

    private String name;
    @Test
    public void test2() throws Exception {
        EntityManager entityManager = entityManagerFactory.createEntityManager();
        entityManager.getTransaction().begin();

        Foo foo=new Foo(1l,"bar");
        entityManager.persist(foo);

        entityManager.getTransaction().commit();
        entityManager.close();

        entityManager = entityManagerFactory.createEntityManager();
        entityManager.getTransaction().begin();

        Foo foo2=new Foo(1l,"baz");
        entityManager.persist(foo2);

        entityManager.getTransaction().commit();
        entityManager.close();
    }

sql> select*from foo;
ID | NAME
1  | bar
1  | baz