Mybatis-Plus快速入门

一、简介

MyBatis-Plus (opens new window)（简称 MP）是一个 MyBatis (opens new window)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能够简化开发，提高效率

这个蓝色的胖鸟就是plus啦~

Mybatis支持很多数据库如常用的mysql, oracle, DB2, H2, HSQL, SQLite，PostgreSQL，SQLServer等等

框架架构

1.1 快速入门

建立数据库插入内容进行测试

我们就用官网上的例子来测试

内容如下：

1.1.1 添加依赖

我们创建SpringBoot工程，导入相关依赖

mybatis-plus-boot-starter

<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>4.0.0modelVersion>
    <parent>
        <groupId>org.springframework.bootgroupId>
        <artifactId>spring-boot-starter-parentartifactId>
        <version>2.6.3version>
        <relativePath/> 
    parent>
    <groupId>com.pyy.mpgroupId>
    <artifactId>mpartifactId>
    <version>0.0.1-SNAPSHOTversion>
    <name>mpname>
    <description>Demo project for Spring Bootdescription>
    <properties>
        <java.version>1.8java.version>
    properties>
    <dependencies>
        <dependency>
            <groupId>com.baomidougroupId>
            <artifactId>mybatis-plus-boot-starterartifactId>
            <version>3.0.5version>
        dependency>
        <dependency>
            <groupId>org.projectlombokgroupId>
            <artifactId>lombokartifactId>
            <optional>trueoptional>
        dependency>
        <dependency>
            <groupId>org.springframework.bootgroupId>
            <artifactId>spring-boot-starter-testartifactId>
            <scope>testscope>
        dependency>
        <dependency>
            <groupId>org.springframework.bootgroupId>
            <artifactId>spring-boot-starterartifactId>
        dependency>
        <dependency>
            <groupId>mysqlgroupId>
            <artifactId>mysql-connector-javaartifactId>
        dependency>
    dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.bootgroupId>
                <artifactId>spring-boot-maven-pluginartifactId>
                <configuration>
                    <excludes>
                        <exclude>
                            <groupId>org.projectlombokgroupId>
                            <artifactId>lombokartifactId>
                        exclude>
                    excludes>
                configuration>
            plugin>
        plugins>
    build>

project>

1.1.2 配置

编写mysql数据源信息

spring:
  datasource:
    username: root
    password: root
    url: jdbc:mysql://localhost:3306/mp
    driver-class-name: com.mysql.cj.jdbc.Driver

mybatis-plus:
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl

编写实体类

package com.pyy.mp.pojo;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

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

编写Mapper接口继承BaseMapper

@Repository和@Controller、@Service、@Component的作用差不多，都是把对象交给spring管理。

@Repository用在持久层的接口上，这个注解是将接口的一个实现类交给spring管理。

package com.pyy.mp.mapper;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.pyy.mp.pojo.User;
import org.springframework.stereotype.Repository;

@Repository
public interface UserMapper extends BaseMapper<User> {

}

在SpringBoot启动类中添加MapperScan注解扫描Mapper类

package com.pyy.mp;

import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@MapperScan("com.pyy.mp")
@SpringBootApplication
public class MpApplication {

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

}

1.1.3 测试

语法糖：用简介的写法表达逻辑

成语：用简介的词语表示句意

package com.pyy.mp;

import com.pyy.mp.mapper.UserMapper;
import com.pyy.mp.pojo.User;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;

import java.util.Arrays;
import java.util.List;

@SpringBootTest
class MpApplicationTests {

//    继承了BaseMapper，所有的方法都来自自己的父类
    @Autowired
    private UserMapper userMapper;


    @Test
    void contextLoads() {
//        参数是一个weapper，条件构造器，这里我们先不用。写成null
        List<User> users = userMapper.selectList(null);
//        ::的写法
//        users.forEach(System.out::println);

//        循环的写法
//        for (User user : users) {
//            System.out.println(user);
//        }

//        lambda表达式的写法
        users.forEach(a->{
            System.out.println(a);
        });
    }
}

结果如下

入门结束，可以看出Mybatis-plus真的很简单，连映射文件sql语句都不用写，只需要引入 starter 工程，并配置 mapper 扫描路径即可

二、核心功能

2.1 通用CRUD

我们通过继承BaseMapper就可以获取到通用的CRUD操作

2.1.1 插入操作

插入操作很简单，做好数据库字段与实体类属性的对应

之后调用通用CRUD中的插入操作

数据库字段如下：

实体类如下：

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {

    @TableId(type = IdType.INPUT)
    private Long id;
    private String name;
    private Integer age;
    private String email;
}

测试

@SpringBootTest
class MpApplicationTests {

//    继承了BaseMapper，所有的方法都来自自己的父类
    @Autowired
    private UserMapper userMapper;


@Test
public void testInsert(){
    User pyy = new User();
    pyy.setId(6L);
    pyy.setName("A");
    pyy.setAge(3);
    pyy.setEmail("[email protected]");
    int result = userMapper.insert(pyy);
    System.out.println(result);
    System.out.println(pyy);
}
    
    
结果如下：
Creating a new SqlSession
SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@6ed16657] was not registered for synchronization because synchronization is not active
JDBC Connection [HikariProxyConnection@1942612200 wrapping com.mysql.cj.jdbc.ConnectionImpl@de8039f] will not be managed by Spring
==>  Preparing: INSERT INTO user ( id, name, age, email ) VALUES ( ?, ?, ?, ? ) 
==> Parameters: 6(Long), A(String), 3(Integer), A@qq.cn(String)
<==    Updates: 1
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@6ed16657]
1
User(id=6, name=A, age=3, email=A@qq.cn)

@TableField

@TableField注解可以指定字段的一些属性，能解决的问题有两个：

1. 对象中的属性名和字段名不一致问题（非驼峰）
2. 对象中属性字段在表中不存在

属性	类型	必须指定	默认值	描述
value	String	否	“”	数据库字段名
exist	boolean	否	true	是否为数据库表字段
select	boolean	否	true	是否进行 select 查询

测试

实体类
package com.pyy.mp.pojo;

import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableName;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@AllArgsConstructor
@NoArgsConstructor
@TableName("user")//表名注解，标识实体类对应的表
public class User {

    @TableId(type = IdType.INPUT)
    private Long id;
    private String name;
    @TableField(value = "age")
    private Integer aage;
    @TableField(select = false)//select不查询这个字段
    private String email;
    @TableField(exist = false)
    private String noexist;

}


测试类
@SpringBootTest
class MpApplicationTests {

//    继承了BaseMapper，所有的方法都来自自己的父类
    @Autowired
    private UserMapper userMapper;


    @Test
    void contextLoads() {
//        参数是一个weapper，条件构造器，这里我们先不用。写成null
        List<User> users = userMapper.selectList(null);
//        ::的写法
//        users.forEach(System.out::println);

//        循环的写法
//        for (User user : users) {
//            System.out.println(user);
//        }

//        lambda表达式的写法
        users.forEach(a->{
            System.out.println(a);
        });
    }

测试结果
Creating a new SqlSession
SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@7979b8b7] was not registered for synchronization because synchronization is not active
JDBC Connection [HikariProxyConnection@1766122814 wrapping com.mysql.cj.jdbc.ConnectionImpl@52e04737] will not be managed by Spring
==>  Preparing: SELECT id,name,age AS aage FROM user 
==> Parameters: 
<==    Columns: id, name, aage
<==        Row: 1, Jone, 18
<==        Row: 2, Jack, 20
<==        Row: 3, Tom, 28
<==        Row: 4, Sandy, 21
<==        Row: 5, Billie, 24
<==        Row: 6, A, 3
<==      Total: 6
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@7979b8b7]
User(id=1, name=Jone, aage=18, email=null, noexist=null)
User(id=2, name=Jack, aage=20, email=null, noexist=null)
User(id=3, name=Tom, aage=28, email=null, noexist=null)
User(id=4, name=Sandy, aage=21, email=null, noexist=null)
User(id=5, name=Billie, aage=24, email=null, noexist=null)
User(id=6, name=A, aage=3, email=null, noexist=null)

2.1.2 更新操作

在MP中更新有两种方式，一种是根据id更新，一种是根据条件更新

QueryWrapper：

继承自 AbstractWrapper ,自身的内部属性 entity 也用于生成 where 条件

--------------------------------------------------------------------------分割线--------------------------------------------------------------

UpdateWrapper

继承自 AbstractWrapper ,自身的内部属性 entity 也用于生成 where 条件及 LambdaUpdateWrapper, 可以通过 new UpdateWrapper().lambda() 方法获取!

根据id更新

    @Test
    public void testUpdate1() {

        User user = new User();
        //更新的字段
        user.setId(6L);
        user.setAge(14);
        user.setName("DDD");
        int i = userMapper.updateById(user);
        System.out.println(i);
    }
    
   Creating a new SqlSession
SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@5e65afb6] was not registered for synchronization because synchronization is not active
JDBC Connection [HikariProxyConnection@1012776440 wrapping com.mysql.cj.jdbc.ConnectionImpl@352c44a8] will not be managed by Spring
==>  Preparing: UPDATE user SET name=?, age=? WHERE id=? 
==> Parameters: DDD(String), 14(Integer), 6(Long)
<==    Updates: 1
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@5e65afb6]
1 

根据条件更新

package com.pyy.mp.pojo;

import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableId;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {

    @TableId(type = IdType.INPUT)
    private Long id;
    private String name;
    private Integer age;
    private String email;

}




根绝QueryWrapper进行更新
@SpringBootTest
class MpApplicationTests {

//    继承了BaseMapper，所有的方法都来自自己的父类
    @Autowired
    private UserMapper userMapper;


	@Test
    public void testUpdate(){
        User user = new User();
        //更新的字段
        user.setAge(14);
        user.setName("CCC");

//        更新的条件
        QueryWrapper<User> wrapper = new QueryWrapper<>();
//        更新的条件是id = 6
        wrapper.eq("id",6);

        int i = userMapper.update(user,wrapper);
        System.out.println(i);
    }
}




Creating a new SqlSession
SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@65a48602] was not registered for synchronization because synchronization is not active
JDBC Connection [HikariProxyConnection@1706939736 wrapping com.mysql.cj.jdbc.ConnectionImpl@1dba4e06] will not be managed by Spring
==>  Preparing: UPDATE user SET name=?, age=? WHERE id = ? 
==> Parameters: CCC(String), 14(Integer), 6(Integer)
<==    Updates: 1
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@65a48602]
1
    
    
    
    
我们还可以根据updateWrapper进行更新
    @Test
    public void testUpdate02(){
        UpdateWrapper<User> wrapper01 = new UpdateWrapper<>();
        wrapper01.eq("id",6).set("name","sadas");

        int i = userMapper.update(null,wrapper01);
        System.out.println(i);
    }


Creating a new SqlSession
SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@28da7d11] was not registered for synchronization because synchronization is not active
JDBC Connection [HikariProxyConnection@728236551 wrapping com.mysql.cj.jdbc.ConnectionImpl@2a3194c6] will not be managed by Spring
==>  Preparing: UPDATE user SET name=? WHERE id = ? 
==> Parameters: sadas(String), 14(Integer), 6(Integer)
<==    Updates: 1
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@28da7d11]
1
    
 

2.1.3 删除操作

deleteById

直接上实例，因为这部分都是api的调用

@Test
public void testDelete01() {
    int i = userMapper.deleteById(6L);
    System.out.println(i);
}

==>  Preparing: DELETE FROM user WHERE id=? 
==> Parameters: 6(Long)
<==    Updates: 1

deleteByMap

接受一个map，mao中的元素会被设置为删除的条件，多个之间为and关系

源码：
int deleteByMap(@Param("cm") Map<String, Object> var1);

@Test
public void testDelete02() {
    HashMap<String, Object> map = new HashMap<>();
    map.put("age",14);
    map.put("name","CCC");
    int i = userMapper.deleteByMap(map);
    System.out.println(i);
}



==>  Preparing: DELETE FROM user WHERE name = ? AND age = ? 
==> Parameters: CCC(String), 14(Integer)
<==    Updates: 1
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@767191b1]
1

delete

@Test
public void testDelete03() {
    QueryWrapper<User> wrapper = new QueryWrapper<>();
    wrapper.eq("name","Jone")
        .eq("age",18);
    userMapper.delete(wrapper);
}

==>  Preparing: DELETE FROM user WHERE name = ? AND age = ? 
    ==> Parameters: Jone(String), 18(Integer)
        <==    Updates: 1

第二种方式

@Test
public void testDelete03() {
    User user = new User();
    user.setAge(20);
    user.setName("Jack");

    //        将实体对象进行包装，包装为操作条件
    QueryWrapper<User> wrapper = new QueryWrapper<>(user);
    userMapper.delete(wrapper);
    }


==>  Preparing: DELETE FROM user WHERE name=? AND age=? 
==> Parameters: Jack(String), 20(Integer)
<==    Updates: 1
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@6eb17ec8]
1

deleteBatchIds

根据id集合批量删除

@Test
    public void testDelete04() {
    	userMapper.deleteBatchIds(Arrays.asList(1L, 11L, 12L));
    }


==>  Preparing: DELETE FROM user WHERE id IN ( ? , ? , ? ) 
==> Parameters: 1(Long), 11(Long), 12(Long)
<==    Updates: 1
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@767191b1]

2.1.4 查询操作

和上面类型，简单的API调用会用即可

selectById

package com.pyy.mp;

import com.pyy.mp.mapper.UserMapper;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;

@SpringBootTest
class MpApplicationTests02 {

    @Autowired
    private UserMapper userMapper;

    @Test
    public void testSelectById(){
        userMapper.selectById(2L);
    }

}


==>  Preparing: SELECT id,name,age,email FROM user WHERE id=? 
==> Parameters: 2(Long)
<==    Columns: id, name, age, email
<==        Row: 2, Jack, 20, test2@baomidou.com
<==      Total: 1

selectBatchIds

根据id集合批量查询

@Test
public void testSelectBatchIds(){
    userMapper.selectBatchIds(Arrays.asList(3L,4L,66L));
}

==>  Preparing: SELECT id,name,age,email FROM user WHERE id IN ( ? , ? , ? ) 
==> Parameters: 3(Long), 4(Long), 66(Long)
<==    Columns: id, name, age, email
<==        Row: 3, Tom, 28, test3@baomidou.com
<==        Row: 4, Sandy, 21, test4@baomidou.com
<==      Total: 2

selectOne

@Test
public void testSelectOne(){
    QueryWrapper<User> userQueryWrapper = new QueryWrapper<>();
    userQueryWrapper.eq("name","Jack");
    userMapper.selectOne(userQueryWrapper);
}



==>  Preparing: SELECT id,name,age,email FROM user WHERE name = ? 
==> Parameters: Jack(String)
<==    Columns: id, name, age, email
<==        Row: 2, Jack, 20, test2@baomidou.com
<==      Total: 1

selectCount

根据Wrapper条件，查询总记录数

@Test
public void testSelectCount(){
    QueryWrapper<User> userQueryWrapper = new QueryWrapper<>();
    userQueryWrapper.gt("age",23);
    Integer integer = userMapper.selectCount(userQueryWrapper);
    System.out.println(integer);
}


==>  Preparing: SELECT COUNT(1) FROM user WHERE age > ? 
==> Parameters: 23(Integer)
<==    Columns: COUNT(1)
<==        Row: 2
<==      Total: 1
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@5c77ba8f]
2

selectList

gt = greater than

lt = little than

其他的类似

@Test
public void testSelectList(){
    QueryWrapper<User> userQueryWrapper = new QueryWrapper<>();
    userQueryWrapper.lt("age",30);
    List<User> users = userMapper.selectList(userQueryWrapper);
    users.forEach(x-> System.out.println(x));
}



==>  Preparing: SELECT id,name,age,email FROM user WHERE age < ? 
==> Parameters: 30(Integer)
<==    Columns: id, name, age, email
<==        Row: 2, Jack, 20, test2@baomidou.com
<==        Row: 3, Tom, 28, test3@baomidou.com
<==        Row: 4, Sandy, 21, test4@baomidou.com
<==        Row: 5, Billie, 24, test5@baomidou.com
<==      Total: 4
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@25290bca]
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)

selectpage

什么是分页查询？

使用SELECT查询时，如果结果集数据量很大，比如几万行数据，放在一个页面显示的话数据量太大，不如分页显示，每次显示100条。

要实现分页功能，实际上就是从结果集中显示第1_{100条记录作为第1页，显示第101}200条记录作为第2页，以此类推。

举例？

SELECT id, name, gender, score
FROM students
ORDER BY score DESC
LIMIT 3 OFFSET 0;

上述查询LIMIT 3 OFFSET 0表示，对结果集从0号记录开始，最多取3条。

Page page = new Page<>(1,1);

查询第一页，查询1条数据

• getTotal() 数据总条数
• getPages() 数据总页数
• getCurrent 当前页数
• getRecords 得到数据

@Test
public void testSelectList(){
    QueryWrapper<User> userQueryWrapper = new QueryWrapper<>();
    userQueryWrapper.lt("age",30);

    Page<User> page = new Page<>(1,1);
    IPage<User> iPage = userMapper.selectPage(page, userQueryWrapper);
    System.out.println(iPage.getTotal());
    System.out.println(iPage.getPages());

    List<User> users = iPage.getRecords();
    users.forEach(x-> System.out.println(x));
}


==>  Preparing: SELECT COUNT(1) FROM user WHERE age < ? 
==> Parameters: 30(Integer)
<==    Columns: COUNT(1)
<==        Row: 4
==>  Preparing: SELECT id,name,age,email FROM user WHERE age < ? LIMIT 0,1 
==> Parameters: 30(Integer)
<==    Columns: id, name, age, email
<==        Row: 2, Jack, 20, test2@baomidou.com
<==      Total: 1
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@46c269e0]
4
4
User(id=2, name=Jack, age=20, email=test2@baomidou.com)

2022-02-18 20:31:03.877  INFO 19944 --- [ionShutdownHook] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Shutdown initiated...
2022-02-18 20:31:03.899  INFO 19944 --- [ionShutdownHook] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Shutdown completed.

Process finished with exit code 0

2.2 条件构造器

Wrapper就是条件构造器

下面我们看它的继承结构

QueryWrapper(LambdaQueryWrapper) 和 UpdateWrapper(LambdaUpdateWrapper) 的父类
用于生成 sql 的 where 条件, entity 属性也用于生成 sql 的 where 条件

2.2.1 allEq

params : key为数据库字段名,value为字段值
null2IsNull : 为true则在map的value为null时调用 isNull方法,为false时则忽略value为null的

@Test
public void testSelectAllEq(){
    Map<String, Object> map = new HashMap<>();
    map.put("name","Jack");
    map.put("age",20);
    map.put("password",null);

    QueryWrapper<User> wrapper = new QueryWrapper<>();
    wrapper.allEq(map,false);
    List<User> users = userMapper.selectList(wrapper);
    users.forEach(x-> System.out.println(x));

}


==>  Preparing: SELECT id,name,age,email FROM user WHERE name = ? AND age = ? 
==> Parameters: Jack(String), 20(Integer)
<==    Columns: id, name, age, email
<==        Row: 2, Jack, 20, test2@baomidou.com
<==      Total: 1

2.2.2 基本比较操作

e:equals

n:not

g:greater

l:little

组合的话意思也组合

:冒号加英文单词可以打出符号哦(:cow)

• eq 等于
• ne 不等于
• gt 大于
• ge 大于等于
• It 小于
• le 小于等于
• between between value1 and value2
• notBetween not between value1 and value2
• in 字段IN（value.get(0),value.get(1),…）

2.2.3 模糊查询

like

• LIKE ‘%值%’
• 例: like("name", "王")—>name like '%王%'

@Test
public void testLike(){
    QueryWrapper<User> wrapper = new QueryWrapper<>();

    wrapper.like("name","J");

    List<User> users = userMapper.selectList(wrapper);
    users.forEach(x-> System.out.println(x));
}

==>  Preparing: SELECT id,name,age,email FROM user WHERE name LIKE ? 
==> Parameters: %J%(String)
<==    Columns: id, name, age, email
<==        Row: 2, Jack, 20, test2@baomidou.com
<==        Row: 9, Jam, 18, test6@qq.cn
<==      Total: 2
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@46c269e0]
User(id=2, name=Jack, age=20, email=test2@baomidou.com)
User(id=9, name=Jam, age=18, email=test6@qq.cn)

2.2.4 排序

orderBy

• 排序：ORDER BY 字段, …
• 例: orderBy(true, true, "id", "name")—>order by id ASC,name ASC

orderByAsc

• 排序：ORDER BY 字段, … ASC(升序)
• 例: orderByAsc("id", "name")—>order by id ASC,name ASC

orderByDesc

• 排序：ORDER BY 字段, … DESC（降序）
• 例: orderByDesc("id", "name")—>order by id DESC,name DESC

@Test
public void testOrder(){
    QueryWrapper<User> wrapper = new QueryWrapper<>();

    wrapper.orderByDesc("age");
    List<User> users = userMapper.selectList(wrapper);
    users.forEach(x-> System.out.println(x));
}

==>  Preparing: SELECT id,name,age,email FROM user ORDER BY age DESC 
==> Parameters: 
<==    Columns: id, name, age, email
<==        Row: 3, Tom, 28, test3@baomidou.com
<==        Row: 5, Billie, 24, test5@baomidou.com
<==        Row: 4, Sandy, 21, test4@baomidou.com
<==        Row: 2, Jack, 20, test2@baomidou.com
<==        Row: 9, Jam, 18, test6@qq.cn
<==      Total: 5
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@5fa23c]
User(id=3, name=Tom, age=28, email=test3@baomidou.com)
User(id=5, name=Billie, age=24, email=test5@baomidou.com)
User(id=4, name=Sandy, age=21, email=test4@baomidou.com)
User(id=2, name=Jack, age=20, email=test2@baomidou.com)
User(id=9, name=Jam, age=18, email=test6@qq.cn)

2022-02-18 21:38:58.700  INFO 1588 --- [ionShutdownHook] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Shutdown initiated...
2022-02-18 21:38:58.725  INFO 1588 --- [ionShutdownHook] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Shutdown completed.

Process finished with exit code 0

2.2.5 逻辑查询

or

主动调用or表示紧接着下一个方法不是用and连接!(不调用or则默认为使用and连接)

例: eq("id",1).or().eq("name","老王")—>id = 1 or name = '小王

and

AND 嵌套

例: and(i -> i.eq("name", "李四").ne("status", "平凡"))—>and (name = '李四' and status <> '平凡')

@Test
public void testOrder(){
    QueryWrapper<User> wrapper = new QueryWrapper<>();

    wrapper.orderByDesc("age");
    List<User> users = userMapper.selectList(wrapper);
    users.forEach(x-> System.out.println(x));
}


==>  Preparing: SELECT id,name,age,email FROM user WHERE name = ? OR age = ? 
==> Parameters: Jack(String), 20(Integer)
<==    Columns: id, name, age, email
<==        Row: 2, Jack, 20, test2@baomidou.com
<==      Total: 1
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@46c269e0]
User(id=2, name=Jack, age=20, email=test2@baomidou.com)

2.2.6 select

在MP查询中，默认查询所有的字段，如果有需要也可以通过select方法进行指定字段。

@Test
public void testSelect(){
    QueryWrapper<User> wrapper = new QueryWrapper<>();
    wrapper.eq("name","Jack")
            .or()
            .eq("age",20)
            .select("id","name","age");
    List<User> users = userMapper.selectList(wrapper);
    users.forEach(x-> System.out.println(x));
}


==>  Preparing: SELECT id,name,age FROM user WHERE name = ? OR age = ? 
==> Parameters: Jack(String), 20(Integer)
<==    Columns: id, name, age
<==        Row: 2, Jack, 20
<==      Total: 1
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@558756be]
User(id=2, name=Jack, age=20, email=null)

2.3 主键策略

@TableId

描述：主键注解

使用位置：实体类主键字段

属性	类型	必须指定	默认值	描述值
value	String	否	“”	主键字段名
type	Enum	否	IdType.NONE	指定主键类型

主键类型：

• AUTO(0) 数据库id自增
• NONE(1) 未设置主键
• INPUT(2) 手动输入
• ID_WORKER(3) 默认的全局唯一id
• UUID(4) 全局唯一id uuid
• ID_WORKER_STR(5) ID_WORKER 字符串表示法

2.3.1 AUTO

数据库设置id字段自动递增

实体类添加注解设置自增

package com.pyy.mp.pojo;

import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableId;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
    @TableId(type = IdType.AUTO)
    private Long id;
    private String name;
    private Integer age;
    private String email;
}

测试

@SpringBootTest
class MpApplicationTests {

//    继承了BaseMapper，所有的方法都来自自己的父类
    @Autowired
    private UserMapper userMapper;
    //测试插入
    @Test
    public void testInsert(){
        User pyy = new User();
        pyy.setName("a");
        pyy.setAge(3);
        pyy.setEmail("[email protected]");
        int result = userMapper.insert(pyy);
        System.out.println(result);
        System.out.println(pyy);
    }
}

.........
Creating a new SqlSession
SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@14823f76] was not registered for synchronization because synchronization is not active
JDBC Connection [HikariProxyConnection@1509506488 wrapping com.mysql.cj.jdbc.ConnectionImpl@1aabf50d] will not be managed by Spring
==>  Preparing: INSERT INTO user ( name, age, email ) VALUES ( ?, ?, ? ) 
==> Parameters: a(String), 3(Integer), a@aa.cn(String)
<==    Updates: 1
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@14823f76]
1
User(id=6, name=a, age=3, email=a@aa.cn)

2.3.2 INPUT

实体类

package com.pyy.mp.pojo;

import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableId;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {

    @TableId(type = IdType.INPUT)
    private Long id;
    private String name;
    private Integer age;
    private String email;
}

测试类

@SpringBootTest
class MpApplicationTests {

//    继承了BaseMapper，所有的方法都来自自己的父类
    @Autowired
    private UserMapper userMapper;

    //测试插入
    @Test
    public void testInsert(){
        User pyy = new User();
        pyy.setId(7L);
        pyy.setName("a");
        pyy.setAge(3);
        pyy.setEmail("[email protected]");
        int result = userMapper.insert(pyy);
        System.out.println(result);
        System.out.println(pyy);
    }
}


...........
Creating a new SqlSession
SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@48840594] was not registered for synchronization because synchronization is not active
JDBC Connection [HikariProxyConnection@2028088629 wrapping com.mysql.cj.jdbc.ConnectionImpl@2e8a1ab4] will not be managed by Spring
==>  Preparing: INSERT INTO user ( id, name, age, email ) VALUES ( ?, ?, ?, ? ) 
==> Parameters: 7(Long), a(String), 3(Integer), a@aa.cn(String)
<==    Updates: 1
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@48840594]
1
User(id=7, name=a, age=3, email=a@aa.cn)

2022-02-17 20:59:30.554  INFO 2152 --- [ionShutdownHook] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Shutdown initiated...
2022-02-17 20:59:30.567  INFO 2152 --- [ionShutdownHook] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Shutdown completed.

Process finished with exit code 0

三、扩展

3.1 自动填充

插入数据时进行填充，也就是为email添加自动填充功能，在新增数据时有效

3.1.1 实体类添加注解

让email字段插入时自动填充数据

@TableField(fill = FieldFill.INSERT)
private String email;

3.1.2 自定义实现类 MyMetaObjectHandler

package com.pyy.mp.handle;

import com.baomidou.mybatisplus.core.handlers.MetaObjectHandler;
import org.apache.ibatis.reflection.MetaObject;
import org.springframework.stereotype.Component;

@Component
public class MyMetaObjectHandler implements MetaObjectHandler {
    //插入数据时填充
    @Override
    public void insertFill(MetaObject metaObject) {
        Object email = getFieldValByName("email", metaObject);
        if (null == email){
            setFieldValByName("email","111111",metaObject);
        }
    }

    //更新数据时填充
    @Override
    public void updateFill(MetaObject metaObject) {

    }
}

3.1.3 测试

@Test
public void testInsert() {
    User pyy = new User();
    pyy.setId(6L);
    pyy.setName("B");
    pyy.setAge(3);

    int result = userMapper.insert(pyy);
    System.out.println(result);
    System.out.println(pyy);
}


==>  Preparing: INSERT INTO user ( name, age, email ) VALUES ( ?, ?, ? ) 
==> Parameters: B(String), 3(Integer), 111111(String)
<==    Updates: 1
 Time：33 ms - ID：com.pyy.mp.mapper.UserMapper.insert
Execute SQL：
    INSERT 
    INTO
        user
        ( name, age, email ) 
    VALUES
        ( 'B', 3, '111111' )

Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@a66e580]
1
User(id=11, name=B, age=3, email=111111, version=null)

3.2 逻辑删除

开发系统时，有时候在实现功能时，删除操作需要实现逻辑删除，所谓逻辑删除就是将数据标记为删除，而并非真正 的物理删除（非DELETE操作），查询时需要携带状态条件，确保被标记的数据不被查询到。这样做的目的就是避免 数据被真正的删除。

就像用户删除购买的订单一样，用户看到实际上是删除了的，但实际上只是逻辑上的删除后台依旧还有数据存在。

3.2.1 修改表结构

3.2.2 修改实体类

@TableLogic
private Integer deleted;

3.2.3 配置文件

新版本的mp可以直接修改yml文件即可

逻辑删除为1，反之为0

mybatis-plus:
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl
  global-config:
    db-config:
      logic-delete-value: 1
      logic-not-delete-value: 0

我用的是3.0的，所以我要在配置类中添加逻辑删除组件

//删除组件
@Bean
public ISqlInjector sqlInjector(){
    return new LogicSqlInjector();
}

3.2.4 测试

@Test
public void testDelete01() {
    userMapper.deleteById(12L);
}

==>  Preparing: UPDATE user SET deleted=1 WHERE id=? AND deleted=0 
==> Parameters: 12(Long)
<==    Updates: 1
 Time：0 ms - ID：com.pyy.mp.mapper.UserMapper.deleteById
Execute SQL：
    UPDATE
        user 
    SET
        deleted=1 
    WHERE
        id=12 
        AND deleted=0

再次查看

12号已被删除

@Test
    void contextLoads() {
        List<User> users = userMapper.selectList(null);
        users.forEach(a -> {
            System.out.println(a);
        });
    }

==>  Preparing: SELECT id,name,age,email,version,deleted FROM user WHERE deleted=0 
==> Parameters: 
<==    Columns: id, name, age, email, version, deleted
<==        Row: 2, Jack, 30, test2@baomidou.com, 2, 0
<==        Row: 3, Tom, 28, test3@baomidou.com, 1, 0
<==        Row: 4, Sandy, 21, test4@baomidou.com, 1, 0
<==        Row: 5, Billie, 24, test5@baomidou.com, 1, 0
<==      Total: 4
 Time：37 ms - ID：com.pyy.mp.mapper.UserMapper.selectList
Execute SQL：
    SELECT
        id,
        name,
        age,
        email,
        version,
        deleted 
    FROM
        user 
    WHERE
        deleted=0

Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@22a6e998]
User(id=2, name=Jack, age=30, email=test2@baomidou.com, version=2, deleted=0)
User(id=3, name=Tom, age=28, email=test3@baomidou.com, version=1, deleted=0)
User(id=4, name=Sandy, age=21, email=test4@baomidou.com, version=1, deleted=0)
User(id=5, name=Billie, age=24, email=test5@baomidou.com, version=1, deleted=0)

实际上只进行了逻辑删除

四、插件

4.1 MybatisX快速开发插件

两个功能：

• Java与XML调回跳转
• Mapper方法自动生成XML

4.2 乐观锁插件

锁的机制：

锁的机制主要用来处理数据冲突之后的解决方式，比如在关系型数据库里，如果一个事物执行的操作对某个数据加了锁，那么只有当这个事物把锁释放，其他的事物才能执行与改锁冲突的操作

4.2.1 悲观锁

正如其名，它指的是对数据被外界修改持保守（悲观），因此在整个数据处理过程中，将数据处于锁定状态。悲观锁的实现，往往依靠数据库提供的锁机制

4.2.2 乐观锁

相对悲观锁而言，乐观锁假设认为数据一般情况下不会有冲突，所以在数据进行提交更新的时候，才会正式对数据的冲突与否进行检测，如果发现了冲突，则让返回用户错误的信息，让用户决定如何去做。乐观锁的实现方式一般是记录数据版本

4.2.3 乐观锁的实现方式

• 取出记录，获取当前Version
• 更新时，带上这个version
• 执行更新时，set version = newVersion where version = oldVersion
• 如果version不对，就更新失败

4.2.4主要适用场景

意图： 当要更新一条记录的时候，希望这条记录没有被别人更新

乐观锁实现方式：

1. 取出记录时，获取当前version
2. 更新时，带上这个version 执行更新时， set version = newVersion where version = oldVersion
3. 如果version不对，就更新失败

插件配置

@Bean
public OptimisticLockerInterceptor optimisticLockerInterceptor(){
    return new OptimisticLockerInterceptor();
}

注解实体类

package com.pyy.mp.pojo;

import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.Version;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {

    @TableId(type = IdType.AUTO)
    private Long id;
    private String name;
    private Integer age;
    private String email;
    @Version
    private Integer version;

}

测试

@Test
public void testUpdate() {
    User user = new User();
    user.setAge(30);
    user.setId(2L);
    user.setVersion(1);//获取到version为1

    userMapper.updateById(user);
}


==>  Preparing: UPDATE user SET age=?, version=? WHERE id=? AND version=? 
==> Parameters: 30(Integer), 2(Integer), 2(Long), 1(Integer)
<==    Updates: 0
 Time：0 ms - ID：com.pyy.mp.mapper.UserMapper.updateById
Execute SQL：
    UPDATE
        user 
    SET
        age=30,
        version=2 
    WHERE
        id=2 
        AND version=1

可以看到sql语句中有version条件，更新时会修改verison为2。

如果再次执行，更新则不成功。这样就避免了多人更新时导致数据的不一致

4.2.5特别说明

1. 支持的数据类型只有:int,Integer,long,Long,Date,Timestamp,LocalDateTime
2. 整数类型下 newVersion = oldVersion + 1
3. newVersion 会回写到 entity 中
4. 仅支持 updateById(id) 与 update(entity, wrapper) 方法
5. 在 update(entity, wrapper) 方法下, wrapper 不能复用!!!

4.3 性能分析插件

@profile 注解的作用是指定类或方法在特定的 Profile 环境生效

4.3.1 在配置类添加插件

package com.pyy.mp.conf;

import com.baomidou.mybatisplus.extension.plugins.PaginationInterceptor;
import com.baomidou.mybatisplus.extension.plugins.PerformanceInterceptor;
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Profile;

@Configuration
@MapperScan("com.pyy.mp")
public class MPConfig {

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

    @Bean
    @Profile({"dev","test"})    //设置dev test环境开启，保证效率
    public PerformanceInterceptor performanceInterceptor(){
        PerformanceInterceptor performanceInterceptor = new PerformanceInterceptor();
        performanceInterceptor.setMaxTime(1);//设置sql执行的最大时间
        performanceInterceptor.setFormat(true);
        return performanceInterceptor;
    }
}

4.3.2 yaml文件

spring:
  datasource:
    username: root
    password: root
    url: jdbc:mysql://localhost:3306/mp
    driver-class-name: com.mysql.cj.jdbc.Driver
  profiles:
    active: dev

4.3.3 测试

可以看到代码被格式化了，但是确报错了。因为我们前面设置了最大查询时间为一毫秒，所以我们可以通过这个插件来进行调优，看看哪些语句执行时间太长

修改后在进行测试

4.4 分页插件

配置类中添加分页插件

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

测试

/**
     * 测试分页查询
     */
    @Test
    public void testPage() {
        //创建page对象
//        传入两个参数，当前页和每页显示记录数
        Page<User> userPage = new Page<>(1,3);
//        调用mp分页查询的方法
//        调用mp分页查询的过程中，底层封装
//        把分页所有数据封装到page对象里面
        userMapper.selectPage(userPage,null);
        System.out.println(userPage.getCurrent());//获取当前页
        System.out.println(userPage.getSize());//每页显示记录数
        System.out.println(userPage.getTotal());//总记录数
        System.out.println(userPage.getPages());//总页数

        System.out.println(userPage.hasNext());//判断是否有下一页
        System.out.println(userPage.hasPrevious());//判断是否有上一页


    }