mybatis会对多参数方法进行特殊处理

例如：查询id=1,name=tom的一条数据

查询接口：

User getUserByIdAndName(Integer id,String name);

//

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!--
namespace:命名空间,指定为接口的全类名
selectUserById：唯一标识
resultType：返回值类型
-->
<mapper namespace="com.yunqing.mybatis.dao.UserMapper">
//这种写法是错误的，mybatis会根据多个参数值封装一个map，在map的key中根据param1....paramN取值或者根据参数索引取值arg0....arg(N-1)

  <!--
　　 <select id="getUserByIdAndName" resultType="com.yunqing.mybatis.bean.User">
        select * from t_user where id = #{id} and name = #{name}
    </select>
  -->

//正确写法 1.根据参数索引

　　 <select id="getUserByIdAndName" resultType="com.yunqing.mybatis.bean.User">
        select * from t_user where id = #{arg0} and name = #{arg1}
    </select>
//正确写法 2.根据参数param
　　

　　 <select id="getUserByIdAndName" resultType="com.yunqing.mybatis.bean.User">
        select * from t_user where id = #{param1} and name = #{param2}
    </select>

</mapper>

建议使用的方法是

<select id="getUserByIdAndName" resultType="com.yunqing.mybatis.bean.User">
        select * from t_user where id = #{id} and name = #{name}
    </select>
这种方法虽然是错误的，但是只要在dao层使用命名参数指定参数名，就是最正确，最明确，最建议的写法：

User getUserByIdAndName(@Param("id")Integer id, @Param("name")String name);

也可以直接传一个pojo对象，或者一个Map,或者自定义To数据传输对象

 

1.map参数

xml中sql

<select id="getUserByMap" resultType="com.yunqing.mybatis.bean.User">
        select * from t_user where id = #{id} and name = #{name}
    </select>

dao

User getUserByMap(Map<String,Object> map);

test.java

@Test
    public void getUserByMap() throws IOException {
        //从xml中获取sqlSessionFactory
        String resource = "conf/mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

        //获取sqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession();
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        Map<String,Object> map = new HashMap<>();
        map.put("id",1);
        map.put("name","tom");
        User user = userMapper.getUserByMap(map);
        System.out.println(user);
        sqlSession.close();
    }