目录
MyBatis-Plus是一款MyBatis的增强工具，在MyBatis的基础上只做增强不做改变，为简化开发、提高效率而生。使用它可以像使用Hibernate一样，对于单表操作只调用方法而不用写SQL即可完成相应数据库的操作，快速开发节省大量时间。而对于多表操作，或者自己想写SQL的时候也可以用原来的MyBatis写SQL的方法来实现。
1 pom.xml
笔者使用的是Spring Boot 2.2.4.RELEASE，相关依赖如下所示（其中引入了Lombok，用来简化Java Model的编程，详见笔者的另一篇文章《Lombok概述》）：
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.2.4.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.hys</groupId>
<artifactId>mybatis-plus</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>mybatis-plus</name>
<description>Demo project for Spring Boot</description>
<properties>
<java.version>1.8</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter</artifactId>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<scope>runtime</scope>
</dependency>
<dependency>
<groupId>com.baomidou</groupId>
<artifactId>mybatis-plus-boot-starter</artifactId>
<version>3.3.1</version>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<optional>true</optional>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
<exclusions>
<exclusion>
<groupId>org.junit.vintage</groupId>
<artifactId>junit-vintage-engine</artifactId>
</exclusion>
</exclusions>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>
2 application.properties
笔者使用的数据库是MySQL 8.0.13，相关的连接配置如下所示（也可以配置MyBatis-Plus的扩展配置，例如主键自增策略、逻辑删除等等。这里只是演示，就都选择默认的配置了）：
#MySQL
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.datasource.url=jdbc:mysql://localhost:3306/user?serverTimezone=UTC&useSSL=false&allowPublicKeyRetrieval=true&useUnicode=true&characterEncoding=UTF-8
spring.datasource.username=root
spring.datasource.password=root
3 启动类
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplication
@MapperScan("com.hys.mybatisplus.mapper")
public class MybatisPlusApplication {
public static void main(String[] args) {
SpringApplication.run(MybatisPlusApplication.class, args);
}
}
在启动类上添加@MapperScan注解，以此来扫描Mapper层。当然也可以在每个Mapper接口中添加@Mapper注解，效果是一样的。
4 Model
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableName;
import lombok.AllArgsConstructor;
import lombok.Builder;
import lombok.Data;
import lombok.NoArgsConstructor;
import java.io.Serializable;
@Data
@NoArgsConstructor
@AllArgsConstructor
@Builder
@TableName("user")
public class User implements Serializable {
private static final long serialVersionUID = -288816356037467194L;
@TableId
private Long userId;
private String name;
private Integer age;
private String email;
}
其中@TableName和@TableId是MyBatis-Plus的注解，用来表示数据库表名和主键。
5 Mapper
import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.hys.mybatisplus.model.User;
public interface UserMapper extends BaseMapper<User> {
}6 Service
import com.baomidou.mybatisplus.extension.service.IService;
import com.hys.mybatisplus.model.User;
public interface UserService extends IService<User> {
}
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import com.hys.mybatisplus.mapper.UserMapper;
import com.hys.mybatisplus.model.User;
import com.hys.mybatisplus.service.UserService;
import org.springframework.stereotype.Service;
@Service
public class UserServiceImpl extends ServiceImpl<UserMapper, User> implements UserService {
}
7 测试类
下面列举了一些用法，完整的功能示例请参考官方文档。
import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.hys.mybatisplus.model.User;
import com.hys.mybatisplus.service.UserService;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;
@SpringBootTest
class MybatisPlusApplicationTests {
@Autowired
private UserService userService;
@Test
void mybatisPlusTest() {
//增
User user = User.builder().name("Robert Hou").age(24).email("[email protected]").build();
userService.save(user);
List<User> list = new ArrayList<>();
list.add(User.builder().name("Emma").age(24).email("[email protected]").build());
list.add(User.builder().name("Joyce").age(18).email("[email protected]").build());
list.add(User.builder().name("Wilson").age(28).email("[email protected]").build());
userService.saveBatch(list, 1000);
//改
user.setAge(25);
userService.updateById(user);
list.forEach(item -> item.setAge(item.getAge() + 1));
userService.updateBatchById(list, 1000);
user.setAge(26);
userService.lambdaUpdate().eq(User::getName, "Robert Hou").update(user);
//查
User byId = userService.getById(1226475999890317314L);
System.out.println(byId);
User robert_hou = userService.getOne(new QueryWrapper<User>().lambda().eq(User::getName, "Robert Hou"));
System.out.println(robert_hou);
List<User> robert_hou1 = userService.lambdaQuery().eq(User::getName, "Robert Hou").list();
robert_hou1.forEach(System.out::println);
List<Long> userIdList = list.stream().map(User::getUserId).collect(Collectors.toList());
userService.listByIds(userIdList);
//删
userService.removeById(6);
userService.removeByIds(userIdList);
userService.remove(new QueryWrapper<User>().lambda().eq(User::getName, "3234"));
}
}
