MyBatis的各种查询功能

查询一个实体类对象
查询一个list集合
查询单个数据
查询一条数据为map的集合

@Test
public void testMybatis() throws IOException {
    SqlSession sqlSession = SqlSessionUtils.getSqlSession();
    ParameterMapper parameterMapper = sqlSession.getMapper(ParameterMapper.class);
    Map<String, Object> result = parameterMapper. getUserByIdToMap(2);
    System.out.println(result);
}

<!--Map<String, Object> getUserByIdToMap(@Param("id") int id)-->
<select id="getUserByIdToMap" resultType="java.util.Map">
    select * from t_user where id = #{id}
</select>

查询多条数据为map的集合

@Test
public void testMybatis() throws IOException {
    SqlSession sqlSession = SqlSessionUtils.getSqlSession();
    ParameterMapper parameterMapper = sqlSession.getMapper(ParameterMapper.class);
    List<Map<String, Object>> result = parameterMapper. getUserByIdToMap();
    result.forEach(mp -> System.out.println(mp));
}

<!--List<Map<String, Object>> getUserByIdToMap()-->
<select id="getUserByIdToMap" resultType="Map">
    select * from t_user
</select>

使用@MapKey注解，定义唯一键，将每条数据转换的map集合作为值

@Test
public void testMybatis() throws IOException {
    SqlSession sqlSession = SqlSessionUtils.getSqlSession();
    ParameterMapper parameterMapper = sqlSession.getMapper(ParameterMapper.class);
    Map<Integer, Object> result = parameterMapper. getUserByIdToMap();
    result.forEach((id, obj) -> System.out.println(obj));
}

1 2	@MapKey("id") Map<Integer, Object> getUserByIdToMap();

<!--Map<Integer, Object> getUserByIdToMap()-->
<select id="getUserByIdToMap" resultType="Map">
    select * from t_user
</select>