hibernate查询&抓取策略优化机制

╰+哭是因爲堅強的太久メ 2021-12-20 03:07 313阅读 0赞

## 一 HQL查询 ##

1 一次存1个客户，10个联系人。执行三次，存3个客户，30个联系人，为分页查询做准备

@Test
            //来3个客户，30个联系人
            public void demo1(){
                Session session=HibernateUtils.getCurrentSession();
                Transaction tx=session.beginTransaction();
                Customer customer=new Customer();
                customer.setCust_name("小白");
                for(int i=0;i<10;i++){
                    LinkMan linkMan=new LinkMan();
                    linkMan.setLkm_name("白白"+i);
    
                    linkMan.setCustomer(customer);
                    customer.getSets().add(linkMan);
                    session.save(linkMan);
                }
                session.save(customer);    
    
                tx.commit();
            }

2 HQL的简单查询

@Test
            //HQL简单查询,一个简单的查询
            public void demo2(){
                Session session=HibernateUtils.getCurrentSession();
                Transaction tx=session.beginTransaction();
                Query query = session.createQuery("from Customer c");//这个Customer是类名
                List<Customer> list = query.list();
                for (Customer customer : list) {
                    System.out.println(customer);
                }
                tx.commit();
            }

3 HQL排序查询,降序查询

@Test
            //HQL排序查询,降序
            public void demo3(){
                Session session=HibernateUtils.getCurrentSession();
                Transaction tx=session.beginTransaction();
                //升序：asc(默认)  降序：desc
                Query query = session.createQuery("from Customer order by cust_id desc");//这个Customer是类名
                List<Customer> list = query.list();
                for (Customer customer : list) {
                    System.out.println(customer);
                }
                tx.commit();
            }

4 HQL的条件查询

@Test
            //HQL
            public void demo4(){
                Session session=HibernateUtils.getCurrentSession();
                Transaction tx=session.beginTransaction();
                //只有一个条件
            /*Query query = session.createQuery("from Customer where cust_name=?");//这个Customer是类名
            query.setParameter(0, "小花");*/
                //多个条件查询
            /*Query query = session.createQuery("from Customer where cust_source=? and cust_name like ?");
            query.setParameter(0, "朋友介绍");
            query.setParameter(1, "%白");*/
                //二 按名称绑定
    
                Query query=session.createQuery("from Customer where cust_source = :a and cust_name like :b");
                query.setParameter("a","网络推广");
                query.setParameter("b","%紫");
    
                List<Customer> list = query.list();
                for (Customer customer : list) {
                    System.out.println(customer);
                }
                tx.commit();
            }

5 HQL的投影查询

@Test
            /**
             * 投影查询
             */
            public void demo5(){
                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);
            }*/
    
                //这里会包含多种类型，用数组接收,查到两列的值了
            /*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，封装到对象里面
                List<Customer> list=session.createQuery("select new Customer(cust_id,cust_name,cust_source) from Customer").list();
                for (Customer customer : list) {
                    System.out.println(customer);
                }
                tx.commit();
            }

6 HQL的分页查询

@Test
            /**
             * 分页查询
             */
            public void demo6(){
                Session session=HibernateUtils.getCurrentSession();
                Transaction tx=session.beginTransaction();
    
                Query query = session.createQuery("from LinkMan");
                query.setFirstResult(0);
                query.setMaxResults(3);//每页显示的条数
                List<LinkMan> list = query.list();
                for (LinkMan linkMan : list) {
                    //要在LinkMan实体类中加上toString
                    System.out.println(linkMan);
                }
                tx.commit();
            }

7 HQL的统计查询

@Test
            public void demo8(){
                //根据客户来源来统计它的个数
            Session session=HibernateUtils.getCurrentSession();
            Transaction tx=session.beginTransaction();
            //既有String类型又有Long类型，用object类型接收
        //    List<Object[]> list=session.createQuery("select cust_source,count(*) from Customer group by cust_source").list();
    
            //根据客户来源统计个数大于等于2的
            List<Object[]> list=session.createQuery("select cust_source,count(*) from Customer group by cust_source having count(*)>=2").list();
            for (Object[]  objects:list) {
                System.out.println(Arrays.toString(objects));
            }
            tx.commit();
        }

8 HQL的多表查询

@Test
        /**
         * HQL的多表查询
         */
        public void demo9(){
            Session session=HibernateUtils.getCurrentSession();
            Transaction tx=session.beginTransaction();
            /*List<Object[]> list = session.createQuery("from Customer c inner join c.sets").list();
            for (Object[] obj: list
                 ) {
                System.out.println(Arrays.toString(obj));
            }*/
            //迫切内链接
            List<Customer> list = session.createQuery("select distinct c from Customer c inner join fetch c.sets").list();
            for (Customer customers: list
                 ) {
                System.out.println(customers);
            }
            tx.commit();
        }

## 二 QBC查询 ##

1 QBC的简单查询

@Test
        /**
         * 简单查询
         */
        public  void demo1(){
            Session session=HibernateUtils.getCurrentSession();
            Transaction tx=session.beginTransaction();
           Criteria criteria= session.createCriteria(Customer.class);
            List<Customer> list = criteria.list();
            for(Customer customer:list){
               System.out.println(customer);
           }
            tx.commit();
        }

2 QBC的排序查询

@Test
        /**
         * 排序查询
         */
        public void demo2(){
            Session session=HibernateUtils.getCurrentSession();
            Transaction tx=session.beginTransaction();
            Criteria criteria = session.createCriteria(Customer.class);
            criteria.addOrder(Order.desc("cust_id"));//asc升序   desc降序
            List<Customer> list = criteria.list();
            for(Customer customer:list){
                System.out.println(customer);
            }
            tx.commit();
        }

3 QBC的分页查询

@Test
        /**
         * 分页查询
         */
        public void demo3(){
            Session session=HibernateUtils.getCurrentSession();
            Transaction tx=session.beginTransaction();
            Criteria criteria = session.createCriteria(LinkMan.class);
            criteria.setFirstResult(0);
            criteria.setMaxResults(10);
            List<LinkMan> list = criteria.list();
            for(LinkMan linkMan:list){
                System.out.println(linkMan);
            }
            tx.commit();
        }

4 QBC的条件查询

@Test
        /**
         * 条件查询
         */
        public void demo4(){
            Session session=HibernateUtils.getCurrentSession();
            Transaction tx=session.beginTransaction();
            Criteria criteria = session.createCriteria(Customer.class);
            /**
             * =        eq
             * >        gt
             * >=       ge
             * <        lt
             * <=       le
             * <>       ne
             * like
             */
            criteria.add(Restrictions.eq("cust_source","广告"));
            criteria.add(Restrictions.like("cust_name","%白"));
            List<Customer> list = criteria.list();
            for(Customer customer:list){
                System.out.println(customer);
            }
            tx.commit();
        }

5 QBC的统计查询

@Test
        /**
         * 统计查询，   一般还是用HQL的，QBC的不常用
         */
        public void demo5(){
            Session session=HibernateUtils.getCurrentSession();
            Transaction tx=session.beginTransaction();
            Criteria criteria = session.createCriteria(Customer.class);
    
            criteria.setProjection(Projections.rowCount());
            Long result= (Long)criteria.uniqueResult();
            System.out.println(result);
            tx.commit();
        }

6 QBC的离线条件查询

@Test
        /**
         * 离线条件查询,在后期的案例中会省很大的时间(相比原来拼接sql语句)
         */
        public void demo6(){
            DetachedCriteria dc = DetachedCriteria.forClass(Customer.class);
            Session session = HibernateUtils.getCurrentSession();
            Transaction tx = session.beginTransaction();
            Criteria criteria = dc.getExecutableCriteria(session);
            List<Customer> list = criteria.list();
            for (Customer customer:list
                 ) {
                System.out.println(customer);
            }
    
            tx.commit();
        }

## 三 抓取策略 ##

抓取策略后续更新！

转载于:https://www.cnblogs.com/bao6/p/10353306.html