--- theme: smartblue --- > 对数据库的操作是我们公司中必不可少的功能，Mybatis Plus是在Mybatis的基础上的增强，使得我们对一些基本的CRUD使用起来更方便等，这篇文章主要讲讲SpringBoot如何去整合Mybatis Plus，并实现基本的CRUD功能。 ### 一、引入相应的依赖 ```xml com.baomidou mybatis-plus-boot-starter 3.5.3.1 mysql mysql-connector-java 8.0.32 ``` 引入`mybatis-plus`的依赖和`mysql`驱动的依赖。 ### 二、进行配置 spring: datasource: url: jdbc:mysql://localhost:3306/mydb?characterEncoding=utf-8&serverTimeZone=UTC username: root password: 123456 driver-class-name: com.mysql.cj.jdbc.Driver mybatis-plus: configuration: log-impl: org.apache.ibatis.logging.stdout.StdOutImpl global-config: db-config: id-type: auto logic-delete-field: deleted logic-delete-value: 1 logic-not-delete-value: 0 `spring.datasource`是对数据库的链接信息的配置 `mybatis-plus`: 1. `configuration.log-impl`: 配置打印sql日志 2. `id-type`: id主键生成策略，auto为自增 3. `logic-delete-field`: 逻辑删除的字段，线上数据库一般要配置逻辑删除 4. `logic-delete-value`: 逻辑删除已删除的值 5. `logic-not-delete-value`: 逻辑删除未删除的值 ### 三、新建数据库表这里我新建一张简单的`user表` ![image.png](https://p6-juejin.byteimg.com/tos-cn-i-k3u1fbpfcp/89926774ff0a4b828f70ec2e902bc516~tplv-k3u1fbpfcp-watermark.image?) sql如下： ```sql DROP TABLE IF EXISTS `user`; CREATE TABLE `user` ( `id` bigint NOT NULL AUTO_INCREMENT, `username` varchar(255) NOT NULL, `age` int NOT NULL, `version` int DEFAULT '1' COMMENT '乐观锁', `create_time` datetime DEFAULT NULL COMMENT '创建时间', `update_time` datetime DEFAULT NULL COMMENT '更新时间', `deleted` int DEFAULT '0' COMMENT '逻辑删除：0：未删除 1：已删除', PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 ``` 可以看到表中有一些建表必须的字段`version`、`create_time`、`update_time`、`deleted`，`version`是乐观锁字段(在高并发更新数据时通过这个字段加锁，更新成功值加1)，`create_time`和`update_time`两个字段我们需要在项目中配置一下`Mybatis Plus`让他在我们新增数据，更新数据时自动插入值，`deleted`逻辑删除字段因为我们已经在yml中配置了，后续我们都不需要再处理。 ### 四、配置 Mybatis Plus 分页插件及乐观锁插件 `config.MybatisPlusConfig：` ```java import com.baomidou.mybatisplus.extension.plugins.MybatisPlusInterceptor; import com.baomidou.mybatisplus.extension.plugins.inner.OptimisticLockerInnerInterceptor; import com.baomidou.mybatisplus.extension.plugins.inner.PaginationInnerInterceptor; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; @Configuration public class MybatisPlusConfig { @Bean public MybatisPlusInterceptor mybatisPlusInterceptor() { MybatisPlusInterceptor mybatisPlusInterceptor = new MybatisPlusInterceptor(); //分页插件 mybatisPlusInterceptor.addInnerInterceptor(new PaginationInnerInterceptor()); //乐观锁插件 mybatisPlusInterceptor.addInnerInterceptor(new OptimisticLockerInnerInterceptor()); return mybatisPlusInterceptor; } } ``` ### 五、配置 Mybatis Plus 自动填充配置 `Mybatis Plus` 自动填充来实现对`create_time`、`update_time`的值自动插入和更新。 1. 新建`handler.mybatisplus.MyMetaObjectHandler`类 2. 该类实现`MetaObjectHandler`接口 3. 并重写`insertFille`和`updateFill`方法具体代码实现如下: `handler.mybatisplus.MyMetaObjectHandler:` ```java import com.baomidou.mybatisplus.core.handlers.MetaObjectHandler; import org.apache.ibatis.reflection.MetaObject; import org.springframework.stereotype.Component; import java.util.Date; @Component public class MyMetaObjectHandler implements MetaObjectHandler { @Override public void insertFill(MetaObject metaObject) { setFieldValByName("createTime", new Date(), metaObject); setFieldValByName("updateTime", new Date(), metaObject); } @Override public void updateFill(MetaObject metaObject) { setFieldValByName("updateTime", new Date(), metaObject); } } ``` ### 六、实现User实体类、UserMapper、UserService 1. User实体类 `domain.entity.User：` ```java import com.baomidou.mybatisplus.annotation.*; import lombok.AllArgsConstructor; import lombok.Data; import lombok.NoArgsConstructor; import lombok.experimental.Accessors; import java.util.Date; @Data @AllArgsConstructor @NoArgsConstructor @Accessors(chain = true) @TableName("user") public class User { @TableId private Long id; private String username; private Integer age; @Version private Integer version; @TableField(fill = FieldFill.INSERT) private Date createTime; @TableField(fill = FieldFill.INSERT_UPDATE) private Date updateTime; private Integer deleted; } ``` `@TableName`：指定实体类对应的表名 `@TableId`：指定为主键，我们配置的是`auto`，即主键自增策略 `@Version`：指定该字段为乐观锁字段，`mybatis plus`会在每次更新时对该字段加1 `@TableField`：指定该值使用我们的自动填充策略，`INSERT`为插入时填充，`INSERT_UPDATE`为插入和更新时填充 2. UserMapper `mapper.UserMapper`: ```java import com.baomidou.mybatisplus.core.mapper.BaseMapper; import com.jk.domain.entity.User; import org.apache.ibatis.annotations.Mapper; @Mapper public interface UserMapper extends BaseMapper { } ``` 继承`Mybatis Plus`提供的`BaseMapper`，已经实现了一些基本的CRUD接口 3. UserService `service.UserService`: ```java public interface UserService { } ``` `service.impl.UserServiceImpl`: ```java import com.jk.service.UserService; import org.springframework.stereotype.Service; @Service public class UserServiceImpl implements UserService { } ``` 先把对应的`service`建好，后面实现`controller`时再一并实现。 ### 七、使用Restful风格实现CRUD功能 1. 创建对应的`DTO`和`VO` 我们在新增和更新时是不需要全部的实体字段，需要创建对应的DTO来接收前端数据，返回时也不需要全部字段，需要对应的Vo对返回前端所需字段 `domain.dto.AddUserDto`: ```java import lombok.AllArgsConstructor; import lombok.Data; import lombok.NoArgsConstructor; @Data @AllArgsConstructor @NoArgsConstructor public class AddUserDto { private String username; private Integer age; } ``` `domain.dto.UpdateUserDto`: ```java import lombok.AllArgsConstructor; import lombok.Data; import lombok.NoArgsConstructor; @Data @AllArgsConstructor @NoArgsConstructor public class UpdateUserDto { private Long id; private String username; private Integer age; } ``` `domain.vo.UserVo`: ```java import lombok.AllArgsConstructor; import lombok.Data; import lombok.NoArgsConstructor; import java.util.Date; @Data @AllArgsConstructor @NoArgsConstructor public class UserVo { private Long id; private String username; private Integer age; private Date createTime; } ``` `domain.vo.PageVo`: ```java import lombok.AllArgsConstructor; import lombok.Data; import lombok.NoArgsConstructor; import java.util.List; @Data @AllArgsConstructor @NoArgsConstructor public class PageVo { private List result; private Long total; } ``` `PageVo`用来处理所有需要分页数据的响应关于统一响应大家可以看 [SpringBoot 中统一响应格式及统一异常处理，你应该这样做](https://juejin.cn/post/7226994337123549242) 关于Bean拷贝大家可以看[SpringBoot 项目中 Bean 拷贝及工具类封装](https://juejin.cn/post/7231033453609009211) 2. `CRUD` 对应的`controller` `controller.UserController`: ```java import com.jk.domain.dto.AddUserDto; import com.jk.domain.dto.UpdateUserDto; import com.jk.service.UserService; import com.jk.domain.vo.ResponseResult; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.web.bind.annotation.*; @RestController @RequestMapping("/user") public class UserController { @Autowired private UserService userService; @PostMapping public ResponseResult addUser(@RequestBody AddUserDto addUserDto) { return userService.addUser(addUserDto); } @PutMapping public ResponseResult updateUser(@RequestBody UpdateUserDto updateUserDto) { return userService.updateUser(updateUserDto); } @DeleteMapping("/{id}") public ResponseResult deleteUser(@PathVariable("id") Long id) { return userService.deleteUser(id); } @GetMapping public ResponseResult getUser(@RequestParam(defaultValue = "1") Integer pageNum, @RequestParam(defaultValue = "10") Integer pageSize) { return userService.getUser(pageNum, pageSize); } } ``` 3. `CRUD` 对应的 `service` `service.UserService`: ```java import com.jk.domain.dto.AddUserDto; import com.jk.domain.dto.UpdateUserDto; import com.jk.domain.vo.ResponseResult; public interface UserService { ResponseResult addUser(AddUserDto addUserDto); ResponseResult updateUser(UpdateUserDto updateUserDto); ResponseResult deleteUser(Long id); ResponseResult getUser(Integer pageNum, Integer pageSize); } ``` 4. `CRUD` 都应 `service实现类` `service.impl.UserServiceImpl`: ```java import com.baomidou.mybatisplus.extension.plugins.pagination.Page; import com.jk.domain.dto.AddUserDto; import com.jk.domain.dto.UpdateUserDto; import com.jk.domain.entity.User; import com.jk.domain.vo.UserVo; import com.jk.mapper.UserMapper; import com.jk.service.UserService; import com.jk.domain.vo.PageVo; import com.jk.domain.vo.ResponseResult; import com.jk.utils.BeanCopyUtils; import org.springframework.beans.BeanUtils; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Service; import java.util.List; @Service public class UserServiceImpl implements UserService { @Autowired private UserMapper userMapper; @Override public ResponseResult addUser(AddUserDto addUserDto) { User user = BeanCopyUtils.copyBean(addUserDto, User.class); userMapper.insert(user); return ResponseResult.okResult(); } @Override public ResponseResult updateUser(UpdateUserDto updateUserDto) { User user = userMapper.selectById(updateUserDto.getId()); BeanUtils.copyProperties(updateUserDto, user); userMapper.updateById(user); return ResponseResult.okResult(); } @Override public ResponseResult deleteUser(Long id) { userMapper.deleteById(id); return ResponseResult.okResult(); } @Override public ResponseResult getUser(Integer pageNum, Integer pageSize) { Page userPage = new Page<>(pageNum, pageSize); userMapper.selectPage(userPage, null); List userVos = BeanCopyUtils.copyBeanList(userPage.getRecords(), UserVo.class); PageVo pageVo = new PageVo(userVos, userPage.getTotal()); return ResponseResult.okResult(pageVo); } } ``` > 关于SpringBoot 整合 Mybatis Plus 实现基本CRUD功能就是这样，其中我们还扩展了不少功能，都是企业开发中必备的，大家如果有什么问题可以评论区留言哦！