MyBatis custom mapping resultMap

       When the field name of the database table is inconsistent with the attribute name in the entity class, you can set a custom mapping through resultMap. Below is a demo of resultMap.

Prepare

Database table
         t_student table

entity class object
         In order to reflect the characteristics of resultMap, the following classes are used as entity class objects.

MyBatis custom mapping resultMap

         Here is a demonstration by querying a piece of data (querying with id as a parameter).
Mapping interface

public interface TMapper {
    
    

    //通过id查询
    T selectStudentById(@Param("id")Integer id);

}

map file

<?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"><!--约束，约束不同xml中所写的标签也不同-->
<mapper namespace="com.xxx.mapper.TMapper"><!--接口-->

    <resultMap id="ttype" type="com.xxx.pojo.T">
        <id property="a" column="id"></id>
        <result property="b" column="name"></result>
        <result property="c" column="age"></result>
        <result property="d" column="sex"></result>
    </resultMap>
<!--    T selectStudentById(@Param("id")Integer id);-->
    <select id="selectStudentById" resultMap="ttype">
        select * from t_student where id=#{id}
    </select>


</mapper>

Explanation
(1) select tag

         Write the query statement in the select tag.
         id: What is written is the method name in the mapped interface.
         resultMap: Writes the value of the id attribute in the resultMap tag.

    <select id="selectStudentById" resultMap="ttype">
        select * from t_student where id=#{id}
    </select>

(2) resultMap label

         The resultMap tag is used to set a custom map.
         id: Indicates the unique ID of the custom mapping.
         type: The type of the entity class to which the queried data is to be mapped.

Subtags of resultMap

         id: Set the mapping relationship of the primary key.
         result: Set the mapping relationship of common fields.
         property: Set the property name in the entity class in the mapping relationship.
         column: Set the field name in the table in the mapping relationship.

	<resultMap id="ttype" type="com.xxx.pojo.T">
        <id property="a" column="id"></id>
        <result property="b" column="name"></result>
        <result property="c" column="age"></result>
        <result property="d" column="sex"></result>
    </resultMap>

test

		/*省略获取MyBatis核心配置文件等*/
		//通过代理模式创建TMapper接口的代理实现类对象
        TMapper mapper = sqlSession.getMapper(TMapper.class);
		//通过id查询
        T t = mapper.selectStudentById(1);
		//输出查询结果
        System.out.println(t);

output result