1.查询一个实体类对象
/* * 根据用户id查询 * */ User GetUserByID(@Param("id") int id);
<!-- User GetUserByID();--> <select id="GetUserByID" resultType="com.li.pojo.User"> select * from USER where id=#{id} </select>
@Test public void GetUserById(){ SqlSession sqlSession = GetSqlSession.getSqlSession(); UserMapper mapper = sqlSession.getMapper(UserMapper.class); User user = mapper.GetUserByID(1); System.out.println(user); }
2.查询一个list集合
/* * 查询所有用户信息 * */ List<User> GetAllUser();
<!-- List<User> GetAllUser();--> <select id="GetAllUser" resultType="com.li.pojo.User"> select * from USER </select>
@Test public void GetAllUser(){ SqlSession sqlSession = GetSqlSession.getSqlSession(); UserMapper mapper = sqlSession.getMapper(UserMapper.class); List<User> list = mapper.getAllUser(); list.forEach(System.out::println); }
3.查询单个数据
/* * 查询单个数据,例如总行数 * */ Integer GetCount();
<!-- Integer GetCount();--> <select id="GetCount" resultType="java.lang.Integer"> select count(*) from user </select>
@Test public void GetCount(){ SqlSession sqlSession = GetSqlSession.getSqlSession(); UserMapper mapper = sqlSession.getMapper(UserMapper.class); Integer integer = mapper.GetCount(); System.out.println(integer); }
4.查询一条数据为map集合
map集合属性不固定，比如有些属性没有值就不会查询出来
/** * 根据用户id查询用户信息为map集合 */ Map<String, Object> getUserToMap(@Param("id") int id);
<!-- Map<String, Object> getUserToMap(@Param("id") int id);--> <select id="getUserToMap" resultType="map"> select * from user where id=#{id} </select>
@Test public void getUserToMap(){ SqlSession sqlSession = GetSqlSession.getSqlSession(); UserMapper mapper = sqlSession.getMapper(UserMapper.class); Map<String, Object> map = mapper.getUserToMap(1); System.out.println(map); }
5.查询多条数据为map集合
方法1
/** * 查询所有用户信息为map集合 * @return * 将表中的数据以map集合的方式查询，一条数据对应一个map；若有多条数据，就会产生多个map集合，此 时可以将这些map放在一个list集合中获取 */ List<Map<String, Object>> getAllUserToMap();
<!--Map<String, Object> getAllUserToMap();--> <select id="getAllUserToMap" resultType="map"> select * from t_user </select>
方法2
/** * 查询所有用户信息为map集合 * @return * 将表中的数据以map集合的方式查询，一条数据对应一个map；若有多条数据，就会产生多个map集合，并 且最终要以一个map的方式返回数据，此时需要通过@MapKey注解设置map集合的键，值是每条数据所对应的 map集合 */ @MapKey("id") Map<String, Object> getAllUserToMap();
<!--Map<String, Object> getAllUserToMap();--> <!-- { 1={password=123456, sex=男, id=1, age=23, username=admin}, 2={password=123456, sex=男, id=2, age=23, username=张三}, 3={password=123456, sex=男, id=3, age=23, username=张三} } --> <select id="getAllUserToMap" resultType="map"> select * from t_user </select>
