Create MyBatis Mappers: Complete Guide

Creating a mapper in MyBatis usually involves the following steps:

1. Create a mapper interface: Start by creating an interface with the typical naming convention of xxxMapper, where xxx represents the name of the corresponding data table or entity class.

public interface UserMapper {
    User selectUserById(int userId);
    void insertUser(User user);
    void updateUser(User user);
    void deleteUser(int userId);
}

1. Create a mapper XML file: Create a XML file with the same name as the mapper interface in the resources directory, to write SQL statements and mapping relationships.

<?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">
<mapper namespace="com.example.mapper.UserMapper">
    <select id="selectUserById" parameterType="int" resultType="com.example.model.User">
        SELECT * FROM user WHERE id = #{userId}
    </select>
    
    <insert id="insertUser" parameterType="com.example.model.User">
        INSERT INTO user (id, name, age) VALUES (#{id}, #{name}, #{age})
    </insert>
    
    <update id="updateUser" parameterType="com.example.model.User">
        UPDATE user SET name = #{name}, age = #{age} WHERE id = #{id}
    </update>
    
    <delete id="deleteUser" parameterType="int">
        DELETE FROM user WHERE id = #{userId}
    </delete>
</mapper>

1. Configure Mapper interface and XML file: Add the scanning and configuration of mapper in MyBatis configuration file (usually mybatis-config.xml).

<configuration>
    <mappers>
        <mapper resource="com/example/mapper/UserMapper.xml"/>
    </mappers>
</configuration>

1. Use mapper: In the code, retrieve the implementation of the mapper interface through MyBatis’s SqlSession object, and then invoke the methods in the interface to execute database operations.

SqlSession sqlSession = sqlSessionFactory.openSession();
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);

User user = userMapper.selectUserById(1);
user.setAge(30);
userMapper.updateUser(user);

sqlSession.commit();
sqlSession.close();

By following the above steps, you can create a mapper in MyBatis and start using it.