MyBatisPlus

准备工作 

        创建web工程，引入依赖

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-test</artifactId>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
</dependency>
<dependency>
    <groupId>com.mysql</groupId>
    <artifactId>mysql-connector-j</artifactId>
    <scope>runtime</scope>
</dependency>

        配置 (yml格式)

server:
  port: 8081

spring:
  datasource:
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://localhost:3306/company?serverTimezone=UTC&rewriteBatchedStatements=true
    username: root
    password: 123456
    type: com.mysql.cj.jdbc.MysqlDataSource

  main:
    banner-mode: off

logging:
  level:
    root: error

        创建实体类

@Data
@NoArgsConstructor
@AllArgsConstructor
public class User {
    private Integer id;
    private String name;
    private String nickname;
    private Integer age;
    private String gender;
    private Integer capital;
    public User(String name, String nickname, Integer age, String gender, Integer capital) {
        this.name = name;
        this.nickname = nickname;
        this.age = age;
        this.gender = gender;
        this.capital = capital;
    }
}

@Data
@NoArgsConstructor
@AllArgsConstructor
public class address {
    private int id;
    private int userId;
    private String country;
    private String province;
    private String city;
}

        创建dao层

@Repository
public interface UserMapper {
}

         创建mapper映射文件

<?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.glaty.studyspringcloud.mapper">

</mapper>

        创建service层，并实现service接口

public interface UserService {
}

@Service
public class UserServiceImpl implements UserService {
}

        创建controller层

@Controller
public class UserController {
}

         创建数据库(使用的是MySQL)以及相应表格

drop database if exists company;
create database if not exists company;

use company;

drop table if exists user;
create table if not exists user(
    id int primary key auto_increment,
    name varchar(10) not null ,
    nickname varchar(20),
    age int,
    gender varchar(2),
    capital int default 0
)auto_increment = 1;

drop table if exists address;
create table if not exists address(
    id int primary key auto_increment,
    user_id int not null ,
    country varchar(15),
    province varchar(15),
    city varchar(15),
    detail varchar(50),
    deleted int default 0 comment '逻辑删除，0为未删除'
);

快速入门

快速开始

引入依赖

        引入MyBatisPlus依赖

<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-boot-starter</artifactId>
    <version>3.5.3.1</version>
</dependency>

 修改mapper

        MybatisPlus提供了一个基础的BaseMapper接口，其中已经实现了绝大部分单表的CRUD。自定义的Mapper继承了这个BaseMapper，就可以直接使用BaseMapper接口定义好的方法。并且可以将@Repository注解改为@Mapper注解

@Mapper
public interface UserMapper extends BaseMapper<User> {
}

测试 

@SpringBootTest
public class MyBatisPlusTest {
    @Autowired
    UserMapper userMapper;
    @Test
    void TestUserMapper() {
        User user1 = new User(1,"张三", "Java高手", 20, "男", 5000);
        User user2 = new User(2,"李四", "JS高手", 19, "女", 5000);
        User user3 = new User(3,"王五", "半个废材", 18, "男", 20000);
        userMapper.insert(user1);
        userMapper.insert(user2);
        userMapper.insert(user3);
        System.out.println(userMapper.selectById(1));
        user1.setCapital(user1.getCapital() + 500);
        userMapper.updateById(user1);
        userMapper.deleteById(user1);
        ArrayList<User> users = new ArrayList<>();
        users.add(user2);
        users.add(user3);
        userMapper.deleteBatchIds(users);
    }
}

常见注解 

        MybatisPlus会根据向BaseMapper接口传入的泛型来推断出表的信息，从而生成SQL。

        默认情况下：

        MybatisPlus会把PO实体的类名驼峰转下划线作为表名

        MybatisPlus会把PO实体的所有变量名驼峰转下划线作为表的字段名，并根据变量类型推断字段类型

        MybatisPlus会把名为id的字段作为主键

        但很多情况下，默认的实现与实际场景不符，因此MybatisPlus提供了一些注解便于我们声明表信息。

@TableName

        表名注解，标识实体类对应的表，用在实体类的定义上

@TableName("user")
public class User {
}

        TableName注解除了指定表名以外，还可以指定很多其它属性：

属性	类型	必须指定	默认值	描述
value	String	否	""	表名
schema	String	否	""	schema