使用jpa的简单的增删查找操作

快来打我* 2023-06-30 09:13 6阅读 0赞

# 保存 #

@Test
        public void  testAdd(){
        
            Customer c = new Customer();
            c.setCustName("船只");
            c.setCustLevel("VIP");
            c.setCustSource("网络");
            c.setCustIndustry("It");
            c.setCustAddress("胡安娜");
            c.setCustPhone("15512234556");
    
            EntityManager em = null;
            EntityTransaction tx = null;
    
            try {
        
                // 获取实体管理对象
                em = JPAUtil.getEntityManager();
                // 获取事务对象
                tx = em.getTransaction();
                // 开启事务
                tx.begin();
                // 执行操作
                em.persist(c);
                // 提交事务
                tx.commit();
            } catch (Exception e) {
        
                // 回滚事务
                tx.rollback();
                e.printStackTrace();
            } finally {
        
                // 释放资源
                em.close();
            }
        }

# 修改 #

@Test
        public void  testMerge(){
        
            EntityManager em = null;
            EntityTransaction tx = null;
    
            try {
        
                em = JPAUtil.getEntityManager();
                tx = em.getTransaction();
                tx.begin();
    
                // 执行操作
                // 必修6l，java.lang.IllegalArgumentException: Provided id of the wrong type for class com.oceanstar.domain.Customer.
                Customer c1 = em.find(Customer.class, 6l);
                c1.setCustName("执行修改操作");
                em.clear(); //把c1对象从缓存中清除出去
                em.merge(c1);
                tx.commit();
            }catch (Exception e){
        
                tx.rollback();
                e.printStackTrace();
            }finally {
        
                em.close();
            }
        }

# 删除 #

/**
    	 * 删除
    	 */
    	@Test
    	public void testRemove() {
        
    		// 定义对象
    		EntityManager em = null;
    		EntityTransaction tx = null;
    		try {
        
    			// 获取实体管理对象
    			em = JPAUtil.getEntityManager();
    			// 获取事务对象
    			tx = em.getTransaction();
    			// 开启事务
    			tx.begin();
    			// 执行操作
    			Customer c1 = em.find(Customer.class, 6L);
    			em.remove(c1);
    			// 提交事务
    			tx.commit();
    		} catch (Exception e) {
        
    			// 回滚事务
    			tx.rollback();
    			e.printStackTrace();
    		} finally {
        
    			// 释放资源
    			em.close();
    		}
    	}

# 根据id查询 #

## 查询一个：使用立即加载策略 ##

find() 方法：根据id查询客户  
![在这里插入图片描述][20200116172150405.png]

// 查询实体的缓存问题
    	@Test
    	public void testGetOne() {
        
    		// 定义对象
    		EntityManager em = null;
    		EntityTransaction tx = null;
    		try {
        
    			// 获取实体管理对象
    			em = JPAUtil.getEntityManager();
    			// 获取事务对象
    			tx = em.getTransaction();
    			// 开启事务
    			tx.begin();
    			// 执行操作
    			Customer c1 = em.find(Customer.class, 1L);
    			Customer c2 = em.find(Customer.class, 1L);
    			System.out.println(c1 == c2);// 输出结果是true，EntityManager也有缓存
    			// 提交事务
    			tx.commit();
    			System.out.println(c1);
    		} catch (Exception e) {
        
    			// 回滚事务
    			tx.rollback();
    			e.printStackTrace();
    		} finally {
        
    			// 释放资源
    			em.close();
    		}
    	}

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poaXpoZW5nZ3Vhbg_size_16_color_FFFFFF_t_70]

## 查询一个：延迟加载 ##

@Test
        public void  testFindOne(){
        
            EntityManager em = null;
            EntityTransaction tx = null;
    
            try {
        
                em = JPAUtil.getEntityManager();
                tx = em.getTransaction();
                tx.begin();
                Customer c1 = em.getReference(Customer.class, 2l);
                Customer c2 = em.getReference(Customer.class, 2l);
                tx.commit();
                System.out.println(c1 == c2);
            }catch (Exception e){
        
                tx.rollback();
                e.printStackTrace();
            }finally {
        
                em.close();
            }
        }

![在这里插入图片描述][20200116172036483.png]  
![在这里插入图片描述][2020011617095166.png]

[20200116172150405.png]: https://img-blog.csdnimg.cn/20200116172150405.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poaXpoZW5nZ3Vhbg_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/20200116170854875.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poaXpoZW5nZ3Vhbg==,size_16,color_FFFFFF,t_70
[20200116172036483.png]: https://img-blog.csdnimg.cn/20200116172036483.png
[2020011617095166.png]: https://img-blog.csdnimg.cn/2020011617095166.png