Hibernate-查询

Posted 2020-10-12 勇往直前

        /**
         *  一、Session查询
         *   get()在无主键的情况下返回null
         *   load()在无主键的情况下会产生异常
         **/

          HibernateSessionFactory.getSession().get(Member.class, "id-a");
          HibernateSessionFactory.getSession().load(Member.class, "id-b");

         二、Query查询 
         //Member是pojo类的名称 
          String hql="from Member as a";  // 返回类型:List<Member>
          String hql="select a.mid from Member as a";//返回类型:List<String>      
          String hql="select a.mid,a.name,a.sex from Member as a";//返回类型:List<Object[]>
          
          //将查询后的结果转换为指定的vo类型,是根据查询返回列的名称自动匹配的
          query.setResultTransformer(new AliasToBeanResultTransformer(Member.class));
        
          
          /**
           * 限定查询
           */
          String kw="hello";
          String hql="from Member as a where a.age=? and a.mid like ?";
          Query query = HibernateSessionFactory.getSession().createQuery(hql);
          //设值 (索引从0开始)
          query.setParameter(0, 10);
          query.setParameter(1, "%"+kw+"%");
          List list = query.list();
          
          /**
           * 统计查询
           */
          String kw="hello";
          String hql="select count(*) from Member as a where a.age=? and a.mid like ?";
          Query query = HibernateSessionFactory.getSession().createQuery(hql);
          //设值 (索引从0开始)
          query.setParameter(0, 10);
          query.setParameter(1, "%"+kw+"%");
          Object obj = query.uniqueResult();
      
          
          /**
           * 分页查询
           */
          int currentPage=1;
          int lineSize=2;
          String hql="from Member as a";
          Query query = HibernateSessionFactory.getSession().createQuery(hql);
          query.setFirstResult((currentPage-1)*lineSize);
          query.setMaxResults(lineSize);
          List list = query.list();
          
          /**
           * 分组查询
           */
          String hql="select a.sex, count(*) from Member as a where a.age=?  group by a.sex";
          Query query = HibernateSessionFactory.getSession().createQuery(hql);
          //设值 (索引从0开始)
          query.setParameter(0, 10);
          List list = query.list();