目录

一、mybatis的各种查询功能

1.1、当查询的数据有多条时使用list来接收

1.2、当查询的数据返回是一个数据类型时

1.3、当查询的数据返回是map类型时

1.4、当查询的数据返回结果为多条时

一、mybatis的各种查询功能

1.1、当查询的数据有多条时使用list来接收

List selectUserById();

        select * from t_user
     
@Test
    public void test10(){
        SqlSession sqlSession = SqlSessionUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        List user = mapper.selectUserById();
        System.out.println("admin = " + user);
    }
 
1.2、当查询的数据返回是一个数据类型时 
Integer queryUserNum();
 
 
        select count(*) from t_user
    

@Test
    public void test11(){
        SqlSession sqlSession = SqlSessionUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        Integer integer = mapper.queryUserNum();
        System.out.println("integer = " + integer);
    }

1.3、当查询的数据返回是map类型时

Map queryUserMap(Integer id);

        select * from t_user where id = #{id}
     
@Test
    public void test12(){
        SqlSession sqlSession = SqlSessionUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        Map map = mapper.queryUserMap(2);
        System.out.println("map = " + map);
    }
 
1.4、当查询的数据返回结果为多条时 
1、使用map类型的list接收
 
List> selectUserListMap();
 

        select * from t_user
    

@Test
    public void test13() {
        SqlSession sqlSession = SqlSessionUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        List> maps = mapper.selectUserListMap();
        maps.forEach(user -> System.out.println("user = " + user));
    }

2、使用注解@MapKey的map集合形式获取

@MapKey("id")
  Map selectUserMap();

        select * from t_user
    

@Test
    public void test14() {
        SqlSession sqlSession = SqlSessionUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        Map map = mapper.selectUserMap();
        System.out.println("map = " + map);
    }