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();
}
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