Implementing Query Optimization

// BAD: orders.forEach(o -> o.getLines())  // each triggers a query
// GOOD:
@Query("select o from Order o join fetch o.lines where o.status = :s")
List<Order> findOpenWithLines(@Param("s") String status);

@Query("select new com.acme.OrderSummary(o.id, o.totalCents) from Order o where o.status = :s")
List<OrderSummary> summarize(@Param("s") String status);

CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Order> q = cb.createQuery(Order.class);
Root<Order> root = q.from(Order.class);
q.select(root).where(cb.equal(root.get("status"), "OPEN"));
em.createQuery(q).getResultList();