[3] resultMap result set mapping

5. Solve the problem of inconsistency between attribute names and field names

1. Specific examples

pojo entity class:

public class User {
    
    

    private Integer uid;
    private String username;
    private String pwd;
}

Database corresponding fields:

Test output results:

    @Test
    public void getUserByID(){
    
    
        SqlSession sqlSession;
        try {
    
    
            sqlSession = MybatisUtils.getSqlSession();
            UserMapper mapper = sqlSession.getMapper(UserMapper.class);
            User user = mapper.getUserByID(2);
            System.out.println(user);
        }finally {
    
    
            MybatisUtils.closeSqlSession();
        }
    }

This happens when the fields are not aligned.

2. Solution

1. Make an alias

    <select id="getUserByID" parameterType="int" resultMap="UserMap">
        select uid,username,password as pwd from users where uid = #{id}
    </select>

2、resultMap

Result set mapping

uid  username  pwd
uid  username  password

    <!--结果集映射-->
    <resultMap id="UserMap" type="User">
        <!--colunm数据库中的字段，properties实体类中的属性-->
        <result column="uid" property="id"/>
        <result column="username" property="name"/>
        <result column="password" property="pwd"/>
    </resultMap>
    <select id="getUserByID" parameterType="int" resultMap="UserMap">
        select * from users where uid = #{id}
    </select>

• resultMap Elements are the most important and powerful elements in MyBatis.
• The design idea of ​​ResultMap is to achieve zero configuration for simple statements, and for more complex statements, only the relationship between the statements needs to be described.
• ResultMap The best part is that although you already know it quite well, you don't need to use them explicitly.