jp QL入门案例-----查询所有

注意：首先要引入依赖，然后要创建配置文件，最后创建实体类，这三项和jpa操作数据库是一样的

一、查询所有

@Test
public void findall() {
    EntityManagerFactory factory = Persistence.createEntityManagerFactory("myjpa");
    EntityManager entityManager = factory.createEntityManager();
    Query query = entityManager.createQuery("from Customer");
    List<Customer> resultList = query.getResultList();
    for (Customer result : resultList) {
        System.out.println(result);
    }
}

二、分页查询

//分页查询
@Test
public void findByPage() {
    EntityManagerFactory factory = Persistence.createEntityManagerFactory("myjpa");
    EntityManager entityManager = factory.createEntityManager();
    Query query = entityManager.createQuery("from Customer");
    query.setFirstResult(0);
    query.setMaxResults(5);
    List<Customer> resultList = query.getResultList();
    for (Customer result : resultList) {
        System.out.println(result);
    }
}

三、模糊查询

//模糊查询
@Test
public void findByname(){
    EntityManagerFactory factory = Persistence.createEntityManagerFactory("myjpa");
    EntityManager entityManager = factory.createEntityManager();
    Query query = entityManager.createQuery("from Customer where cust_name like ?");
    query.setParameter(1,"%金%");
    List<Customer> resultList = query.getResultList();
    for (Customer result:resultList){
        System.out.println(result);
    }

}
四、排序查询

//排序查询
@Test
public void findByOrder(){
    EntityManagerFactory factory = Persistence.createEntityManagerFactory("myjpa");
    EntityManager entityManager = factory.createEntityManager();
    Query query = entityManager.createQuery("from Customer order by cust_id desc");//asc是升序
    List<Customer> resultList = query.getResultList();
    for (Customer result:resultList){
        System.out.println(result);
    }
}

五、聚合函数查询

//聚合函数查询
@Test
public void findBycount(){
    EntityManagerFactory factory = Persistence.createEntityManagerFactory("myjpa");
    EntityManager entityManager = factory.createEntityManager();
    //查询总条数
    Query query = entityManager.createQuery("select count(*) from Customer");
    //查询id的总和
    entityManager.createQuery("select sum(cust_id) from Customer");
    Object singleResult = query.getSingleResult();
    System.out.println(singleResult);

}

六、条件查询

//条件查询
@Test
public void findById() {
    EntityManagerFactory factory = Persistence.createEntityManagerFactory("myjpa");
    EntityManager entityManager = factory.createEntityManager();
    Query query = entityManager.createQuery("from Customer where cust_id=?");
    query.setParameter(1, 3L);
    Customer singleResult = (Customer) query.getSingleResult();
    System.out.println(singleResult);
    entityManager.close();

}