Hibernate学习笔记9（HQL查询）

淡淡的烟草味﹌ 2021-11-05 05:38 256阅读 0赞

# **Hibernate的查询方式** #

在Hibernate中提供了很多种的查询的方式。Hibernate共提供了五种查询方式。

*  **1.OID查询**  
    OID检索：Hibernate根据对象OID（主键）进行检索
    
     *  使用get方法  
        Customer customer = session.get(Customer.class,1l)
     *  使用load方法  
        Customer customer = session.load(Customer.class,1l)
 *  **2.对象导航查询**  
    对象导航检索：Hibernate根据一个已经查询到的对象，获得其关联对象的一种查询方式
    
        LinkMan linkman=session.get(LinkMan.class,1l)
         Customer customer=linkman.getCustomwr()
          
         Customer customer=session.get(Customer.class,2l)
         Set<LinkMan> LinkMans=customer.getLinkMans()
 *  **3.HQL检索**  
    HQL查询;Hibernate Query Language，Hibernate的查询语言，是一种面向对象方式的查询语言，语法类似SQL,通过session,createQuery(),用于接收一个HQL进行查询方式  
    （1）初始化数据

public void demo1() {
    		Session session = HibernateUtils.getCurrentSession();
    		Transaction tx = session.beginTransaction();
    		//创建一个客户
    		Customer customer = new Customer();
    		customer.setCust_name("李向文");
    		
    		for(int i=1;i<=10;i++) {
    			LinkMan linkman = new LinkMan();
    			linkman.setLkm_name("王东"+i);
    			linkman.setCustomer(customer);
    			
    			customer.getLinkMans().add(linkman);
    			session.save(linkman);
    		}
    		session.save(customer);
    		
    		tx.commit();
    	}

（2）HQL的简单查询

@Test
    	/*HQL的简单查询
    	 * 
    	 */
    	public void demo2() {
    		Session session = HibernateUtils.getCurrentSession();
    		Transaction tx = session.beginTransaction();
    		
    		Query query = session.createQuery("from Customer");
    		List<Customer> list = query.list();
    		//sql中支持*号写法 select * from cst_customer;但HQL中不支持*号写法
    		//Query query = session.createQuery("select *from Customer");会报错
    		//List<Customer> list = query.list();
    		
    		for(Customer customer : list) {
    			System.out.println(customer);
    		}
    		
    		
    		tx.commit();
    		
    	}

![在这里插入图片描述][20190808103116177.png]  
（3）HQL的排序查询

@Test
    	/*HQL的排序查询
    	 * 
    	 */
    	public void demo4() {
    		Session session = HibernateUtils.getCurrentSession();
    		Transaction tx = session.beginTransaction();
    		//排序查询
    		//默认情况 升序
    		//List<Customer> list = session.createQuery("from Customer order by cust_id ").list();
    		//设置降序排序  desc降序  asc升序
    		List<Customer> list = session.createQuery("from Customer order by cust_id desc ").list();
    		for(Customer customer : list) {
    			System.out.println(customer);
    		}
    		tx.commit();
    	}

![在这里插入图片描述][20190808110302204.png]  
（4）HQL的条件查询

/*HQL的条件查询
    	 * 
    	 */
    	public void demo5() {
    		Session session = HibernateUtils.getCurrentSession();
    		Transaction tx = session.beginTransaction();
    		//条件查询
    		//1.按位置绑定
    		//一个条件
    		//Query query = session.createQuery("from Customer where cust_name = ?");
    		//query.setParameter(0, "李冰");
    		//List<Customer> list = query.list();
    		//多个条件
    		/*Query query = session.createQuery("from Customer where cust_source = ? and cust_name like ?");
    		query.setParameter(0, "小广告");
    		query.setParameter(1, "李%");
    		List<Customer> list = query.list();*/
    		//2.按名称绑定
    		Query query = session.createQuery("from Customer where cust_source = :aaa and cust_name like :bbb");
    		//设置参数
    		query.setParameter("aaa", "朋友推荐");
    		query.setParameter("bbb", "李%");
    		List<Customer> list = query.list();
    		
    		for(Customer customer : list) {
    			System.out.println(customer);
    		}
    		tx.commit();
    	}

![在这里插入图片描述][20190808113653587.png]  
（5）HQL的投影查询

@Test
    	/*HQL的投影查询
    	 * 
    	 */
    	public void demo6() {
    		Session session = HibernateUtils.getCurrentSession();
    		Transaction tx = session.beginTransaction();
    		//投影查询
    		//单个属性
    		/*List<Object> list = session.createQuery("select c.cust_name from Customer c ").list();
    		for(Object object : list) {
    			System.out.println(object);
    		}*/
    		//多个属性：
    		/*List<Object[]> list = session.createQuery("select c.cust_name,c.cust_source from Customer c ").list();
    		for(Object[] objects : list) {
    			System.out.println(Arrays.toString(objects));
    		}*/
    		//查询多个属性，但我想封装到对象中
    		List<Customer> list = session.createQuery("select new Customer(cust_name,cust_source) from Customer").list();
    		for(Customer customer : list) {
    			System.out.println(customer);
    		}
    		
    		
    		tx.commit();
    	}

![在这里插入图片描述][2019080813225622.png]  
（6）HQL的分页查询

@Test
    	/*HQL的分页查询
    	 * 
    	 */
    	public void demo7() {
    		Session session = HibernateUtils.getCurrentSession();
    		Transaction tx = session.beginTransaction();
    		Query query = session.createQuery("from LinkMan");
    		query.setFirstResult(10);
    		query.setMaxResults(10);
    		List<LinkMan> list = query.list();
    		
    		for(LinkMan linkman : list) {
    			System.out.println(linkman);
    		}
    		
    		
    		tx.commit();
    	}

（7）HQL的分组查询

@Test
    	/*HQL的分组统计查询
    	 * 
    	 */
    	public void demo8() {
    		Session session = HibernateUtils.getCurrentSession();
    		Transaction tx = session.beginTransaction();
    		//聚合作用的使用：count（），max（），min（），avg（），sum（）
    		Object object = session.createQuery("select count(*) from Customer").uniqueResult();
    		System.out.println(object);
    		
    		//分组统计
    		List<Object[]> list = session.createQuery("select cust_source,count(*) from Customer group by cust_source").list();
    		
    		
    		for(Object[] objects : list) {
    			System.out.println(Arrays.toString(objects));
    		}
    		tx.commit();
    	}

[20190808103116177.png]: /images/20211104/4dd0f6779810441ab36b5dbb0d79a93e.png
[20190808110302204.png]: /images/20211104/dea0ec4a5bf94dee91b32be725866879.png
[20190808113653587.png]: /images/20211104/90ebc0650a06461593bd62257e99958f.png
[2019080813225622.png]: /images/20211104/2e0e6fbb8ce84349a0ba270e7be36914.png