Hibernate的检索方式

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Hibernate的检索方式分为五种:

1.对象导航检索.根据已加载的对象,调用方法.导航到其他对象

Customer c=session.get(Customer.class,2);   c.getOrders().size()

2.OID检索:按照对象的OID检索对象:通过get/load方法查询指定的对象,要通过OID检索,也就是id

get和load的区别:
1.get是立即加载,load方法是延迟加载策略,当我们获取加载出来的对象的相关属性时,才发送sql,查询返回的是一个代理对象.
2.get方法查询的时候,如果这个对象不存在,会返回null;
load方法查询时,如果对象不存在,会报错.

3.HQL(Hibernate Query Language),面向对象的查询语言

Select/update/delete…… from …… where …… group by …… having …… order by …… asc/desc

基本步骤:1.得到session  2.编写hql语句   3.通过session.createQuery(hql) 创建query对象   4.为Query对象设置条件参数     5.执行list()查询所有,他返回的是list集合.uniqueResult()返回的是唯一查询结果.

//基本检索
    @Test
    public void test5(){
        Session session = HibernateUtils.openSession();
        session.beginTransaction();
        //1.编写hql语句
        String hql = "from Customer" ;
        //2.获得query,获得list集合
        Query query = session.createQuery(hql);
        List<Customer> list = query.list();
        
        System.out.println(list.get(0));
        
        session.getTransaction().commit();
        session.close();
    }
//排序检索
    @Test
    public void test6(){
        Session session = HibernateUtils.openSession();
        session.beginTransaction();
        String hql ="from Order Order by money asc";
        Query query = session.createQuery(hql);
        List<Order> list = query.list();
        System.out.println(list);
        session.getTransaction().commit();
        session.close();
    }
    //条件检索
    @Test
    public void test7(){
        Session session = HibernateUtils.openSession();
        session.beginTransaction();
        String hql ="from Order where money > ? ";
        Query query = session.createQuery(hql).setParameter(0, 2000d);
        List<Order> list = query.list();
        System.out.println(list);
        session.getTransaction().commit();
        session.close();
    }
    //分页检索
        @Test
        public void test8(){
            Session session = HibernateUtils.openSession();
            session.beginTransaction();
            String hql = "from Order";
            Query query = session.createQuery(hql);
            //每页显示6,得到第二页的数据
            query.setFirstResult((2-1)*6);
            query.setMaxResults(6);
            List<Order> list = query.list();
            System.out.println(list);
            session.getTransaction().commit();
            session.close();
        }
        //分组统计检索
                @Test
                public void test9(){
                    Session session = HibernateUtils.openSession();
                    session.beginTransaction();
                    //分组统计每一个人的订单总价
                    String hql = "select c.name,sum(money) from Order group by c ";
                    Query query = session.createQuery(hql);
                    
                    List<Object[]> list = query.list();
                    for (Object[] objects : list) {
                        for ( Object o: objects) {
                            System.out.println(o);
                        }
                    }
                    //System.out.println(list);
                    session.getTransaction().commit();
                    session.close();
                }
                //投影检索,必须在Customer类创建无参(创建有参就不会提供默认的无参)和有参构造
                @Test
                public void test10(){
                    Session session = HibernateUtils.openSession();
                    session.beginTransaction();
                    String hql = "select new Customer(id,name) from Customer ";
                    Query query = session.createQuery(hql);
                    List<Customer> list = query.list();
                    System.out.println(list);
                    session.getTransaction().commit();
                    session.close();
                }
                @Test
                //命名检索,在Customer类定义@NamedQuery(name="myHql",query="from Customer")
                //把创建Query封装到实体类的namedQuery
                public void test11(){
                    Session session = HibernateUtils.openSession();
                    session.beginTransaction();
                    Query query = session.getNamedQuery("myHql");
                    List<Customer> list = query.list();
                    System.out.println(list);
                    session.getTransaction().commit();
                    session.close();
                }

4.QBC检索方式,使用QBC(Query by Criteria)API来检索对象，这种API封装了基于字符串形式的查询语句，提供了更加面向对象的查询接口.步骤: 

1.通过session得到一个Criteria对象: session.getCriteria();  2.设置条件:add方法设置条件,Retrictions获取Criteria实例(大于等于等)

3.调用list(),获取集合数据.

@Test
    public void test001() {
        // 基本检索----查询所有Customer
        Session session = HibernateUtils.openSession();
        session.beginTransaction();
        Criteria criteria = session.createCriteria(Customer.class);
        List l = criteria.list();
        System.err.println(l);
        session.getTransaction().commit();
        session.close();
    }

    @Test
    public void test002() {
        // 排序检索----查询订单信息,根据订单的价格进行排序
        Session session = HibernateUtils.openSession();
        session.beginTransaction();
        Criteria criteria = session.createCriteria(Order.class);
        // 这个路径的Order是排序,是为了区别domain中的Order
        criteria.addOrder(org.hibernate.criterion.Order.asc("money"));
        List l = criteria.list();
        System.err.println(l);
        session.getTransaction().commit();
        session.close();
    }

    @Test
    public void test003() {
        // 条件检索----查询客户名称为张某:张_
        Session session = HibernateUtils.openSession();
        session.beginTransaction();
        Criteria criteria = session.createCriteria(Customer.class);
        SimpleExpression like = Restrictions.like("name", "张_");
        criteria.add(like);
        Customer c = (Customer) criteria.uniqueResult();
        // System.err.println(l);
        // 查询订单价格在2050以上,并且客户时张某
        Criteria cri = session.createCriteria(Order.class);
        SimpleExpression gt = Restrictions.gt("money", 2050d);
        SimpleExpression eq = Restrictions.eq("c", c);
        LogicalExpression and = Restrictions.and(gt, eq);
        cri.add(and);
        List list = cri.list();
        System.out.println(list);
        session.getTransaction().commit();
        session.close();
    }

    @Test
    public void test004() {
        // 分页检索----
        Session session = HibernateUtils.openSession();
        session.beginTransaction();
        Criteria criteria = session.createCriteria(Order.class);
        criteria.setFirstResult((2 - 1) * 6);
        criteria.setMaxResults(6);
        List<Order> list = criteria.list();
        System.out.println(list);
        session.getTransaction().commit();
        session.close();
    }

    @Test
    public void test005() {
        // 统计分组检索----统计订单总数
        Session session = HibernateUtils.openSession();
        session.beginTransaction();
        Criteria criteria = session.createCriteria(Order.class);
        /*
         * List list = criteria.setProjection(Projections.rowCount()).list();
         * System.out.println(list);
         */
        // 2.统计订单的总价格---分组统计根据客户
        // List list =
        // criteria.setProjection(Projections.sum("money")).list();--总价格
        criteria.setProjection(Projections.projectionList()
                .add(Projections.sum("money"))
                .add(Projections.groupProperty("c")));
        List<Object[]> list = criteria.list();
        for (Object[] objects : list) {
            for (Object obj : objects) {
                System.out.println(obj);
            }
        }
        session.getTransaction().commit();
        session.close();
    }

    @Test
    //离线条件检索
    public void test006() {
        //1.得到一个Detached
        DetachedCriteria dc = DetachedCriteria.forClass(Customer.class);
        dc.add(Restrictions.like("name","张_"));
        //2.生成Criteria执行操作
        Session session = HibernateUtils.openSession();
        session.beginTransaction();
        Criteria criteria = dc.getExecutableCriteria(session);
        List<Customer> list = criteria.list();
        System.out.println(list);
        session.getTransaction().commit();
        session.close();
    }

5.使用本地数据库的sql语言

//执行本地sql
    @Test
    public void test1(){
        Session session = HibernateUtils.openSession();
        session.beginTransaction();
        SQLQuery sqlQuery = session.createSQLQuery("select*from t_customer");
        sqlQuery.addEntity(Customer.class);//将查询结果绑定到指定对象
        //sqlQuery.setParameter(position, val);设置参数
        List list = sqlQuery.list();
        System.out.println(list);
        session.getTransaction();
        session.close();
    }
    //测试执行本地sql的命名查询
    @Test
    public void test2(){
        Session session = HibernateUtils.openSession();
        session.beginTransaction();
        Query query = session.getNamedQuery("findCustomer");
        List list = query.list();
        System.out.println(list);
        session.getTransaction();
        session.close();
        //由于hibernate执行sql语句后,不知道结果该如何封装,所以用下面的注解
        //@SqlResultSetMapping(name="mapping",entities={@EntityResult(entityClass=Customer.class,fields={@FieldResult(name="id",column="id"),@FieldResult(name="name",column="name")})})
        //@NamedNativeQuery(name="findCustomer",query="select*from t_customer",resultSetMapping="mapping")
}

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