MyBatis-Plus简介

MyBatis-Plus（简称 MP）是一个 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。

MyBatis-Plus官网

依赖

<!--lombok-->
<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <optional>true</optional>
</dependency>
<!--mybatis-plus-->
<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-boot-starter</artifactId>
    <version>3.0.6</version>
</dependency>
<!--mysql-->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <scope>runtime</scope>
    <version>8.0.13</version>
</dependency>

创建并配置数据库

use mydb;

DROP TABLE IF EXISTS `user`;

CREATE TABLE `user` (
  `id`    int(11) NOT NULL AUTO_INCREMENT,
  `name`  varchar(255)     DEFAULT NULL,
  `age`   varchar(255)     DEFAULT NULL,
  `email` varchar(255)     DEFAULT NULL,
  PRIMARY KEY (`id`)
)
  ENGINE = MyISAM
  AUTO_INCREMENT = 19
  DEFAULT CHARSET = utf8;

INSERT INTO `user` (id, name, age, email)
VALUES (1, 'Jone', 18, 'test1@baomidou.com'),
       (2, 'Jack', 20, 'test2@baomidou.com'),
       (3, 'Tom', 28, 'test3@baomidou.com'),
       (4, 'Sandy', 21, 'test4@baomidou.com'),
       (5, 'Billie', 24, 'test5@baomidou.com');

INSERT INTO `user` (id, name, age, email)
VALUES (6, 'Jone6', 10, 'test1@baomidou.com'),
       (7, 'Jack7', 22, 'test2@baomidou.com'),
       (8, 'Tom8', 283, 'test3@baomidou.com'),
       (9, 'Sandy9', 241, 'test4@baomidou.com'),
       (10, 'Billie0', 224, 'test5@baomidou.com');

ALTER TABLE user MODIFY id BIGINT(20) AUTO_INCREMENT;

application.properties：

# database
spring.datasource.url=jdbc:mysql://127.0.0.1:3306/mydb?useUnicode=true&characterEncoding=utf8&useSSL=false&serverTimezone=GMT
spring.datasource.username=root
spring.datasource.password=admin
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver

编写实体类

@Data
public class User {
    private Long id;
    private String name;
    private Integer age;
    private String email;
}

编写Mapper类

public interface UserMapper extends BaseMapper<User> {

}

在 Spring Boot 启动类中添加 @MapperScan 注解，扫描 Mapper 文件夹：

@SpringBootApplication
@MapperScan("com.example.demo.mapper")
public class DemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }

}

开始使用

@Resource
private UserMapper userMapper;

@Test
public void testSelect() {
    System.out.println(("----- selectAll method test ------"));
    List<User> userList = userMapper.selectList(null);
    Assert.assertEquals(5, userList.size());
    userList.forEach(System.out::println);
}

打印结果：

----- selectAll method test ------
User(id=1, name=Jone, age=18, email=test1@baomidou.com)
User(id=2, name=Jack, age=20, email=test2@baomidou.com)
User(id=3, name=Tom, age=28, email=test3@baomidou.com)
User(id=4, name=Sandy, age=21, email=test4@baomidou.com)
User(id=5, name=Billie, age=24, email=test5@baomidou.com)

分页

添加分页配置类

//Spring boot方式
@EnableTransactionManagement
@Configuration
@MapperScan("com.example.demo.mapper")
public class MybatisPlusConfig {

    /**
     * 分页插件
     */
    @Bean
    public PaginationInterceptor paginationInterceptor() {
        return new PaginationInterceptor();
    }
}

测试：

@Test
public void test1(){
    System.out.println("----- baseMapper 自带分页 ------");
    Page<User> page = new Page<>(1, 5);
    IPage<User> userIPage = userMapper.selectPage(page,null);
    Assert.assertSame(page, userIPage);
    System.out.println("总条数 ------> " + userIPage.getTotal());
    System.out.println("当前页数 ------> " + userIPage.getCurrent());
    System.out.println("当前每页显示数 ------> " + userIPage.getSize());
    List<User> records = userIPage.getRecords();
    records.forEach(System.out::println);
    System.out.println("----- baseMapper 自带分页 ------");
}

打印：

----- baseMapper 自带分页 ------
总条数 ------> 10
当前页数 ------> 1
当前每页显示数 ------> 5
User(id=1, name=Jone, age=18, email=test1@baomidou.com)
User(id=2, name=Jack, age=20, email=test2@baomidou.com)
User(id=3, name=Tom, age=28, email=test3@baomidou.com)
User(id=4, name=Sandy, age=21, email=test4@baomidou.com)
User(id=5, name=Billie, age=24, email=test5@baomidou.com)
----- baseMapper 自带分页 ------

条件查找并分页

添加mapper类中方法

public interface UserMapper extends BaseMapper<User> {

    /*按照年龄查找*/
    IPage<User> selectAge10(Page page, @Param("age") Integer age);

}

添加mapper的xml，映射mapper类

<?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.example.demo.mapper.UserMapper">
    <select id="selectAge10" resultType="com.example.demo.entity.User">
        SELECT * FROM user WHERE age=#{age}
    </select>
</mapper>

添加mapper的xml文件扫描

#
mybatis-plus.mapper-locations=classpath:/mapper/*.xml

测试

/*分页查找指定年龄*/
@Test
public void test3() {
    System.out.println("----- baseMapper 自带分页 ------");
    Page<User> page = new Page<>(1, 5);
    IPage<User> userIPage = userMapper.selectAge10(page, 20);
    Assert.assertSame(page, userIPage);
    System.out.println("总条数 ------> " + userIPage.getTotal());
    System.out.println("当前页数 ------> " + userIPage.getCurrent());
    System.out.println("当前每页显示数 ------> " + userIPage.getSize());
    List<User> records = userIPage.getRecords();
    records.forEach(System.out::println);
    System.out.println("----- baseMapper 自带分页 ------");
}

打印：

----- baseMapper 自带分页 ------
总条数 ------> 2
当前页数 ------> 1
当前每页显示数 ------> 5
User(id=2, name=Jack, age=20, email=test2@baomidou.com)
User(id=10, name=Billie0, age=20, email=test5@baomidou.com)
----- baseMapper 自带分页 ------