文档08_mybatis三个查询方法VIP

1、1. MyBatis 中常用的三个查询方法1.1 selectList如果没有查到任用于查询多条数据的情况, 返回值是一个 list 集合.何数据,返回没有元素的集合(空集合,不是null)1.2 selectOne用于查询单条数据的情况, 返回值是一个对象. 如果没有查到任何数 据, 返回nullTestpublic void testSelectOne() throws IOException InputStream is = Resources.getResourceAsStream(mybatis-cfg.xml);SqlSessionFactory factory = newSqlS

2、essionFactoryBuilder().build(is);Testpublic void testSelectList() throws IOException InputStream is = Resources.getResourceAsStream(mybatis-cfg.xml);SqlSessionFactory factory = newSqlSessionFactoryBuilder().build(is); SqlSession session = factory.openSession();List list = session.selectList(com.bjsx

3、t.mapper.UserMapper.selAll);System.out.println(list);for (User user : list) System.out.println(user);session.close();1.3 selectMap用于查询多条数据的情况, 多条数据要形成一个Map 集合. 需要指定 哪个属性作为key. 如果查不到, 返回一个空map 集合(不是null)Testpublic void testSelectMap() throws IOException InputStream is = Resources.getResourceAsStream(

4、mybatis-cfg.xml);SqlSessionFactory factory = newSqlSessionFactoryBuilder().build(is); SqlSession session = factory.openSession();Map map = session.selectMap(com.bjsxt.mapper.UserMapper.selAll, id);System.out.println(map); Set set = map.keySet(); for (Integer k : set) System.out.println(map.get(k);session.close();SqlSession session = factory.openSession();User user = session.selectOne(com.bjsxt