mapper的两种写法

1.mapper接口+mapper.xml文件的方式(xml可以理解为实现类，由xml文件，mapper配置就写xml文件；没有xml文件就写接口类)

mapper接口如下

package com.mapper;

import com.pojo.Teacher;

import java.util.List;

public interface TeacherMapper {
    
    public List<Teacher> findAll();

}

mapper.xml如下
注意：namespace的值一般为接口所在的包名加接口名
"com.mapper.TeacherMapper"

<?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.mapper.TeacherMapper">

    <resultMap id="teacherMap" type="Teacher">
        <id property="id" column="id"/>
        <result property="name" column="t_name"/>
    </resultMap>
    <select id="findAll" resultMap="teacherMap">
        select * from tb_teacher
    </select>
</mapper>

在整体的配置文件中，要写xml的全名

<mapper resource="mapper/teacherMapper.xml"/>

若接口和xml文件在同一包下，并且名字相同，则可以写接口的全名**

<mapper class="com.mapper.TeacherMapper"/>

2.mapper接口加注解的方式

直接将mapper.xml配置文件用注解的方式写在接口中，所以只有一个mapper的接口,其中result代表resultMap
mapper接口

package com.mapper;

import com.pojo.Teacher;
import org.apache.ibatis.annotations.Result;
import org.apache.ibatis.annotations.Results;
import org.apache.ibatis.annotations.Select;

import java.util.List;

public interface TeacherMapper {

    @Select("select * from tb_teacher")
    @Results({
            @Result(property = "id",column = "id"),
            @Result(property = "name",column = "t_name")
    })
    public List<Teacher> findAll();

}

在整体的配置文件中，要写接口的全名

<mapper class="com.mapper.TeacherMapper"/>s

调用的两种写法

1.使用SqlSession的selectOne，selectList，selectMap方法

package com.dao;

import com.pojo.Teacher;
import com.util.MyBatisUtil;
import org.apache.ibatis.session.SqlSession;

import java.util.List;

public class UserDao {
    private SqlSession sqlSession = MyBatisUtil.getSqlSession();

    public List<Teacher> findAll(){
        List<Teacher> list = sqlSession.selectList("com.mapper.TeacherMapper.findAll");
        return list;
    }
}

2.调用mapper接口的方法

package com.dao;

import com.mapper.TeacherMapper;
import com.pojo.Teacher;
import com.util.MyBatisUtil;
import org.apache.ibatis.session.SqlSession;

import java.util.List;

public class TeacherDao {
    private SqlSession sqlSession = MyBatisUtil.getSqlSession();
    
    public List<Teacher> findAll(){
        TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);
        List<Teacher> list = mapper.findAll();
        return list;
    }
    
}