Sprawozdanie:

Podczas opracowywania ostatniego zadania zauważyłem, że podczas FetchType.LAZY wykonują się dwa selecty, podczas FetchType.EAGER tylko jeden.
Fetch type Eager to opozycja do Lazy, Eager załaduje wszystkie relacje od razu, lazy niestety "rozbije" proces na drobne części.

By otrzymać statementsy napisałem krótki dodatkowy test:

    @Test
    public void testooo() {

        EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory(ConfigConsts.PERSISTANCE_UNIT_NAME);
        EntityManager entityManager = entityManagerFactory.createEntityManager();

        Client theClient = entityManager.find(Client.class, 1);

        for (Order orders : theClient.getOrders()) {
        	orders.getDescription();
        }

        // EAGER - wykonuje się JEDEN select.
        /*
         *
         * select
         * 		client0_.id as id1_1_0_,
         * 		client0_.address as address2_1_0_,
         * 		client0_.name as name3_1_0_,
         * 		client0_.client_no as client_n4_1_0_,
         * 		client0_.ssn as ssn5_1_0_,
         * 		orders1_.CLIENT_ID as CLIENT_I5_1_1_,
         * 		orders1_.id as id1_0_1_,
         * 		orders1_.id as id1_0_2_,
         * 		orders1_.CLIENT_ID as CLIENT_I5_0_2_,
         * 		orders1_.ORDER_DATE as ORDER_DA2_0_2_,
         *		orders1_.ORDER_DESC as ORDER_DE3_0_2_,
         *		orders1_.ORDER_NO as ORDER_NO4_0_2_
         *		from clients client0_
         *		left outer join ORDERS orders1_
         *		on client0_.id=orders1_.CLIENT_ID
         *		where client0_.id=?
         *
         */

        // LAZY - wykonują się 2x selecty.

    	/*
    	 * select
    	 * 		client0_.id as id1_1_0_,
    	 * 		client0_.address as address2_1_0_,
    	 * 		client0_.name as name3_1_0_,
    	 * 		client0_.client_no as client_n4_1_0_,
    	 * 		client0_.ssn as ssn5_1_0_
    	 * 		from clients client0_
    	 * 		where client0_.id=?
    	 *
				select
					orders0_.CLIENT_ID as CLIENT_I5_1_0_,
					orders0_.id as id1_0_0_,
					orders0_.id as id1_0_1_,
					orders0_.CLIENT_ID as CLIENT_I5_0_1_,
					orders0_.ORDER_DATE as ORDER_DA2_0_1_,
					orders0_.ORDER_DESC as ORDER_DE3_0_1_,
					orders0_.ORDER_NO as ORDER_NO4_0_1_

					from ORDERS orders0_
					where orders0_.CLIENT_ID=?
    	 *
    	 */

    }