介绍

MyBatis 的真正强大在于它的语句映射，这是它的魔力所在。由于它的异常强大，映射器的 XML 文件就显得相对简单。如果拿它跟具有相同功能的 JDBC 代码进行对比，你会立即发现省掉了将近 95% 的代码。MyBatis 致力于减少使用成本，让用户能更专注于 SQL 代码。
官网中文文档：https://www.mybatis.net.cn/sqlmap-xml.html

Mapper映射文件使用

application.properties 添加配置

# mapper.xml 配置文件路径
mybatis-plus.mapper-locations=classpath:mapper/*.xml
# 配置XML映射文件中指定的实体类别名路径
mybatis-plus.type-aliases-package=cn.qvtu.web.domain

在项目mapper目录中创建Mapper文件

mapper.xml文件放在resources/mapper目录中

UserMapper.xml 文件

简单增删改查SQL配置，namespace对应 UserMapper.java 的包名

<?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="cn.qvtu.web.mapper.UserMapper">

    <select id="selectUserById" parameterType="long" resultType="User">
        SELECT * FROM user WHERE id = #{id}
    </select>

    <insert id="insertUser" parameterType="User" >
        insert into user (id,name,age,email)
        values (#{id},#{name},#{age},#{email})
    </insert>

    <update id="updateUser" parameterType="User" >
        update user set
        name = #{name},
        age = #{age},
        email = #{email}
        where id = #{id}
    </update>

    <delete id="deleteUser" parameterType="long">
        delete from user where id = #{id}
    </delete>

    <select id="selectUserList" parameterType="User" resultType="User">
        SELECT * FROM user WHERE 1=1
        <if test="name != null and name != ''">
            AND name = #{name}
        </if>
        <if test="email != null and email != ''">
            AND email = #{email}
        </if>
        <if test="age != null">
            AND age = #{age}
        </if>
    </select>

</mapper>

UserMapper.java 文件

UserMapper.xml文件中 每个id名称对应UserMapper.java的方法名称

@Mapper
public interface UserMapper extends BaseMapper<User> {

    public User selectUserById(Long id);

    public void updateUser(User user);

    public void insertUser(User user);

    public void deleteUser(Long id);

    public List<User> selectUserList(User user);
}

IUserService 文件

定义具体业务逻辑的接口

public interface IUserService extends IService<User> {

    public User selectUserById(Long id);

    public void updateUser(User user);

    public void insertUser(User user);

    public void deleteUser(Long id);

    public List<User> selectUserList(User user);

}

UserServiceImpl文件

实现具体业务逻辑的接口，调用UserMapper实现数据的CRUD

@Service
public class UserServiceImpl extends ServiceImpl<UserMapper,User> implements IUserService {

    @Autowired
    private UserMapper userMapper;

    @Override
    public User selectUserById(Long id) {
        return userMapper.selectUserById(id);
    }

    @Override
    public void updateUser(User user) {
         userMapper.updateUser(user);
    }

    @Override
    public void insertUser(User user) {
        userMapper.insertUser(user);
    }

    @Override
    public void deleteUser(Long id) {
        userMapper.deleteUser(id);
    }

    @Override
    public List<User> selectUserList(User user) {
        return userMapper.selectUserList(user);
    }

}

UserController 文件

前端访问控制器

@RestController
@RequestMapping("/user")
public class UserController {

    @Autowired
    private IUserService userService;

    @GetMapping("/select")
    public User select(Long id){
        return userService.selectUserById(id);
    }

    @GetMapping("/insert")
    public String insert(User user){
        userService.insertUser(user);
        return "insert SUCCESS";
    }

    @GetMapping("/update")
    public String update(User user){
        userService.updateUser(user);
        return "update SUCCESS";
    }

    @GetMapping("/delete")
    public String delete(Long id){
        userService.deleteUser(id);
        return "delete SUCCESS";
    }

    @GetMapping("/selectList")
    public List<User> select(User user){
        return userService.selectUserList(user);
    }

}