为OneToMany关系构造JPA查询

EntityManager entityManager = ...;
CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
CriteriaQuery<ParentEntity> criteriaQuery = criteriaBuilder.createQuery(ParentEntity.class);
Root<ParentEntity> root = criteriaQuery.from(ParentEntity.class);
Join<ParentEntity, ChildEntity> children = root.join(ParentEntity_.children, JoinType.LEFT);
Predicate predicate = criteriaBuilder.equal(root.get(ParentEntity_.id), parentId);
criteriaQuery.where(predicate);
TypedQuery<ParentEntity> query = entityManager.createQuery(criteriaQuery);
ParentEntity parentEntity = query.getSingleResult();

EntityManager entityManager = ...;
String jpql = "SELECT p FROM ParentEntity p LEFT JOIN FETCH p.children WHERE p.id = :parentId";
TypedQuery<ParentEntity> query = entityManager.createQuery(jpql, ParentEntity.class);
query.setParameter("parentId", parentId);
ParentEntity parentEntity = query.getSingleResult();