JPA JPQL

JPQL

• JPQL：Java Persistence Query Language
• 用于完成复杂查询，EntityManager.find 方法只能完成根据 id 查询
• 和 SQL 语法基本一致，但 JPQL 不支持 select *
• 查出来的实体对象的均处于 Managed 状态，可以用于 remove，setter，remove 之后还可以调用 persist 保存
• 注意分页查询的写法

JPQL 测试

查询全部 from Student

@Test
public void test1() {
    EntityManagerFactory factory = Persistence.createEntityManagerFactory("myJpa");
    EntityManager em = factory.createEntityManager();
    EntityTransaction tx = em.getTransaction();
    tx.begin();

    String jpql = "from Student";
    Query query = em.createQuery(jpql);
    List list = query.getResultList();
    /*

    Hibernate:
        select
            student0_.sid as sid1_0_,
            student0_.sage as sage2_0_,
            student0_.sname as sname3_0_
        from
            Student student0_

     */
    for (Object o : list) {
        System.out.println(o);
    }
    /*

    Student{sid=1, sname='刘备', sage=24}
    Student{sid=2, sname='关羽', sage=23}
    Student{sid=3, sname='张飞', sage=21}

     */

    tx.commit();
    em.close();
    factory.close();
}

逆序查询全部 from Student order by sid desc

@Test
public void test2() {
    EntityManagerFactory factory = Persistence.createEntityManagerFactory("myJpa");
    EntityManager em = factory.createEntityManager();
    EntityTransaction tx = em.getTransaction();
    tx.begin();

    String jpql = "from Student order by sid desc";
    Query query = em.createQuery(jpql);
    List list = query.getResultList();
    /*

    Hibernate:
        select
            student0_.sid as sid1_0_,
            student0_.sage as sage2_0_,
            student0_.sname as sname3_0_
        from
            Student student0_
        order by
            student0_.sid desc

     */
    for (Object o : list) {
        System.out.println(o);
    }

    /*

    Student{sid=3, sname='张飞', sage=21}
    Student{sid=2, sname='关羽', sage=23}
    Student{sid=1, sname='刘备', sage=24}

     */

    tx.commit();
    em.close();
    factory.close();
}

分页查询 from Student

@Test
public void test3() {
    EntityManagerFactory factory = Persistence.createEntityManagerFactory("myJpa");
    EntityManager em = factory.createEntityManager();
    EntityTransaction tx = em.getTransaction();
    tx.begin();

    String jpql = "from Student";
    Query query = em.createQuery(jpql);
    query.setFirstResult(1);
    query.setMaxResults(2);
    List list = query.getResultList();
    /*

    Hibernate:
        select
            student0_.sid as sid1_0_,
            student0_.sage as sage2_0_,
            student0_.sname as sname3_0_
        from
            Student student0_ limit ?,
            ?

     */
    for (Object o : list) {
        System.out.println(o);
    }

    /*

    Student{sid=2, sname='关羽', sage=23}
    Student{sid=3, sname='张飞', sage=21}

     */

    tx.commit();
    em.close();
    factory.close();
}

统计查询 select count(*) from Student

@Test
public void test4() {
    EntityManagerFactory factory = Persistence.createEntityManagerFactory("myJpa");
    EntityManager em = factory.createEntityManager();
    EntityTransaction tx = em.getTransaction();
    tx.begin();

    String jpql = "select count(*) from Student";
    Query query = em.createQuery(jpql);
    Long count = (Long) query.getSingleResult();
    /*

    Hibernate:
        select
            count(*) as col_0_0_
        from
            Student student0_

     */
    System.out.println(count); // 3

    tx.commit();
    em.close();
    factory.close();
}

条件查询 from Student where sname like ?1

@Test
public void test5() {
    EntityManagerFactory factory = Persistence.createEntityManagerFactory("myJpa");
    EntityManager em = factory.createEntityManager();
    EntityTransaction tx = em.getTransaction();
    tx.begin();

    String jpql = "from Student where sname like ?1";
    Query query = em.createQuery(jpql);
    query.setParameter(1, "关%");
    List list = query.getResultList();
    /*

    Hibernate: 
        select
            student0_.sid as sid1_0_,
            student0_.sage as sage2_0_,
            student0_.sname as sname3_0_ 
        from
            Student student0_ 
        where
            student0_.sname like ?

     */
    for (Object o : list) {
        System.out.println(o);
    }

    /*

    Student{sid=2, sname='关羽', sage=23}

     */

    tx.commit();
    em.close();
    factory.close();
}