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 setname = #{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 {@Autowiredprivate UserMapper userMapper;@Overridepublic User selectUserById(Long id) {return userMapper.selectUserById(id);}@Overridepublic void updateUser(User user) {userMapper.updateUser(user);}@Overridepublic void insertUser(User user) {userMapper.insertUser(user);}@Overridepublic void deleteUser(Long id) {userMapper.deleteUser(id);}@Overridepublic 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 {@Autowiredprivate 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);}}