jpa入門案例----使用jpa對數據庫進行查詢、刪除、修改操作

配置文件、依賴、實體類的創建方法在上一篇博客《使用jpa對數據庫進行添加數據》的博客中寫的有

 

一、查詢操作

 @Test
    //根據id查找
    public void find(){
        EntityManagerFactory factory = Persistence.createEntityManagerFactory("myjpa");
        EntityManager entityManager = factory.createEntityManager();
        Customer customer = entityManager.getReference(Customer.class, 6L);//第一個參數是實體類名，第二個參數是id
//也可以使用下面這個方法查詢
        Customer customer1 = entityManager.find(Customer.class, 8L);
    }


二、刪除操作
要先查詢在刪除

 @Test
    public void testDelete(){
        //創建工廠
        EntityManagerFactory factory = Persistence.createEntityManagerFactory("myjpa");
        //創建一個EntityManager對象
        EntityManager entityManager = factory.createEntityManager();
        //使用entityManager對象開啟事物
        EntityTransaction transaction = entityManager.getTransaction();
        transaction.begin();
        Customer customer = entityManager.find(Customer.class, 1L);
//        System.out.println(customer);
        //執行刪除操作
        entityManager.remove(customer);
        transaction.commit();
    }

三、修改
同樣要先進查詢操作，然后再進行修改操作

//修改
@Test
public void update(){
    EntityManagerFactory factory = Persistence.createEntityManagerFactory("myjpa");
    EntityManager entityManager = factory.createEntityManager();
    EntityTransaction transaction = entityManager.getTransaction();
    //開啟事物
    transaction.begin();
    //先查詢
    Customer customer = entityManager.find(Customer.class, 8L);
    //修改
    customer.setCustName("aaa");
    //執行修改命令
    entityManager.persist(customer);
    //提交事物
    transaction.commit();
    //釋放資源
    entityManager.close();
    factory.close();
    
}