Spring Boot学习篇(五)

Spring Boot学习篇(五)

mybatis-plus使用

1.1 配置pom.xml文件

<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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0modelVersion>

    <groupId>org.examplegroupId>
    <artifactId>boot-plusartifactId>
    <version>1.0-SNAPSHOTversion>
    
    <parent>
        <artifactId>spring-boot-starter-parentartifactId>
        <groupId>org.springframework.bootgroupId>
        <version>2.7.2version>
    parent>
    
    <dependencies>
        
        <dependency>
            <groupId>org.springframework.bootgroupId>
            <artifactId>spring-boot-starter-webartifactId>
        dependency>
        
        <dependency>
            <groupId>mysqlgroupId>
            <artifactId>mysql-connector-javaartifactId>
        dependency>
        
        <dependency>
            <groupId>org.projectlombokgroupId>
            <artifactId>lombokartifactId>
        dependency>

        
        <dependency>
            <groupId>com.baomidougroupId>
            <artifactId>mybatis-plus-boot-starterartifactId>
            <version>3.5.1version>
        dependency>
        
        <dependency>
            <groupId>org.springframework.bootgroupId>
            <artifactId>spring-boot-starter-testartifactId>
        dependency>

        
        <dependency>
            <groupId>com.baomidougroupId>
            <artifactId>mybatis-plus-generatorartifactId>
            <version>3.5.3version>
        dependency>
        <dependency>
            <groupId>org.apache.velocitygroupId>
            <artifactId>velocity-engine-coreartifactId>
            <version>2.3version>
        dependency>
    dependencies>
project>

1.2 在java文件夹下面创建com包.zlz包,其目录结构如下所示

1.3 在zlz包下创建PlusStart类,其内容如下所示

package com.zlz;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class PlusStart {
    public static void main(String[] args) {
        SpringApplication.run(PlusStart.class);
    }
}

1.4 在zlz包下创建代码生成器类MyGenerator

1.4.0 复制java文件夹绝对路径小技巧

1.4.1 内容如下

package com.zlz;

import com.baomidou.mybatisplus.generator.FastAutoGenerator;
import com.baomidou.mybatisplus.generator.config.OutputFile;
import com.baomidou.mybatisplus.generator.config.rules.DateType;

import java.util.Collections;

public class MyGenerator {
    public static void main(String[] args) {
        FastAutoGenerator.create("jdbc:mysql://127.0.0.1:3305/db0618", "root", "root")
                .globalConfig(builder -> {
                    builder.author("zlz") // 设置作者
                            .dateType(DateType.ONLY_DATE) // 时间策略,日期以什么样子的类型去生成
                            .outputDir("F:\\boot\\boot-plus\\src\\main\\java"); // 指定输出目录
                })
                .packageConfig(builder -> {
                    builder.parent("com.zlz") // 设置父包名
                            .pathInfo(Collections.singletonMap(OutputFile.xml, "F:\\boot\\boot-plus\\src\\main\\resources\\mapper")); // 设置mapperXml生成路径,
                    // 注意:这个mapper文件夹是可以不存在的,运行该main方法会自动创建的
                })
                .strategyConfig(builder -> {
                     //开启lombok
                    builder.entityBuilder().enableLombok();
                    //覆盖现有文件
                    builder.entityBuilder().fileOverride();
                    builder.addInclude("songs"); // 设置需要生成的表名,想一次性生成多张表,就用逗号隔开,如:addInclude("songs","music")
                })
                .execute();
    }
}

1.5 运行MyGenerator类方法

1.5.1 运行前目录结构

1.5.2 运行后

a 弹出一个如下所示的文件资源管理器,直接叉掉即可

b 运行后目录结构

1.6.微改一下生成的实体类Songs

package com.zlz.entity;

import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableId;
import java.io.Serializable;
import java.util.Date;

import lombok.*;

/**
 * 

 * 
 * 
 *
 * @author zlz
 * @since 2023-01-02
 */
//①改动地方1
@AllArgsConstructor
@NoArgsConstructor
@Data
public class Songs implements Serializable {

    private static final long serialVersionUID = 1L;

    @TableId(value = "id", type = IdType.AUTO)
    private Integer id;

    private String singerName;

    private String album;

    private String albumImg;

    private String name;
    //②改动地方2,调成日期形式,就不用转型了
    private String releaseDate;
}

1.7.在resources文件夹下创建application.yml,其内容如下所示

spring:
  datasource
    url: jdbc:mysql://127.0.0.1:3305/db0618
    driver-class-name: com.mysql.cj.jdbc.Driver
    username: root
    password: root

mybatis-plus:
  type-aliases-package: com.zlz.entity #实体别名扫描
#配置日志 查看具体的sql执行语句
logging:
  level:
    com.zlz.mapper: debug

1.8 在zlz包下创建config包,并创建PlusConfig类

1.8.1 目录结构如下所示

1.8.2 PlusConfig类的内容如下所示

package com.zlz.config;

import org.mybatis.spring.annotation.MapperScan;
import org.springframework.context.annotation.Configuration;

@Configuration
@MapperScan("com.zlz.mapper")//mapper接口扫描，@MapperScan也可以放在启动类PlusStart上面(启动类也算配置类)
public class PlusConfig {
}

1.9.测试类环境准备

import com.zlz.PlusStart;
import com.zlz.service.ISongsService;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;

@SpringBootTest(classes = PlusStart.class,
    webEnvironment = SpringBootTest.WebEnvironment.NONE)
public class MyTest {
    @Autowired
    ISongsService songsService;
}

1.10 查询

A 根据主键查询单条

a 示例代码

@Test
public void findOne(){
    Songs byId = songsService.getById(666);
    System.out.println(byId);
}

b.运行截图

B 查询全部

a 示例代码

 @Test
    public void findAll(){
        List<Songs> list = songsService.list();
        for (Songs songs : list) {
            System.out.println(songs);
        }
    }

b 运行截图

C 带条件的查询(queryWrapper)

a 相等查询

a.1 示例代码

//带上条件的查询(使用场景:商城商品的关键字搜索)
@Test
public void findByCondition(){
    //查询条件构造器
    String search="张学友";
    QueryWrapper<Songs> qw = new QueryWrapper<>();
    //第一个参数是条件,如果条件为真就带上第三个参数,为假就不带上,第二个参数是表的字段名
    qw.eq(search!=null, "singer_name",search);
    List<Songs> list = songsService.list(qw);
    for (Songs songs : list) {
        System.out.println(songs);
    }
}

a.2 运行截图

b 范围查询between

b.1 示例代码

  @Test
    public void findByCondition(){
        //范围查找between
        QueryWrapper<Songs> qw = new QueryWrapper<>();
        qw.between("release_date", "2000-1-1","2020-1-1");
        List<Songs> list = songsService.list(qsw);
        for (Songs songs : list) {
            System.out.println(songs);
        }
    }

b.2 运行截图

c 模糊查询 like

c.1 示例代码

  @Test
    public void findByCondition(){
        //查询条件构造器
        QueryWrapper<Songs> qw = new QueryWrapper<>();
        //查询歌曲表中歌手名字以张开头的所有歌手信息
        qw.likeRight("singer_name", "张");
        List<Songs> list = songsService.list(qw);
        for (Songs songs : list) {
            System.out.println(songs);
        }
    }

c.2 运行截图

e 查询指定的一些列

e.1 示例代码

public void findByCondition(){
        //查询条件构造器
        QueryWrapper<Songs> qw = new QueryWrapper<>();
        //查询某些列是用逗号去进行分开,然后查到了的数据才有值,没有查到的数据就都是null值
        qw.select("id,name");
        List<Songs> list = songsService.list(qw);
        for (Songs songs : list) {
            System.out.println(songs);
        }
    }

e.2 运行截图

f 分组查询

f.1 示例代码

@Test
    public void findByGroup(){
        //统计歌曲表中每个歌手唱了多少首歌
        //① 创建QueryWrapper对象
        QueryWrapper<Songs> qw = new QueryWrapper<>();
        //② 指定分组字段
        qw.groupBy("singer_name");
        //下面的select方法相当于的sql语句是 select singer_name,count(*) num from songs group by singer_name;
        //③指定要查询出来的列
        qw.select("singer_name,count(*) num");
        //因为是多条数据,一条数据就相当于一个map,所以需要用List>来进行接受
        //④使用listMaps方法去进行查询
        List<Map<String, Object>> maps = songsService.listMaps(qw);
        for (Map<String, Object> map : maps) {
            System.out.println(map);
        }
    }

f.2 日志显示最终使用的sql语句

f.3 查询出来的结果展示

g 排序查询

g.1 示例代码

//排序的使用
@Test
public void findByOrder(){
    //把歌曲表按照日期降序排列
    QueryWrapper<Songs> qw = new QueryWrapper<>();
    //如果想要指定多个字段排序,那么可以使用逗号隔开,如orderByDesc("字段1,字段2...")
    qw.orderByDesc("release_date");
    songsService.list(qw).forEach(System.out::println);
}

9.2 运行截图

D 分页查询

a 在PlusConfig中加入如下代码

@Bean
public MybatisPlusInterceptor mybatisPlusInterceptor() {
    MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
    //设置分页插件,别的拦截器也是addInnerInterceptor加入进去
    PaginationInnerInterceptor pi = new PaginationInnerInterceptor();
    pi.setDbType(DbType.MYSQL);//设置数据库类型为MySQL
    pi.setOverflow(true);//溢出分页处理,默认是false不处理,需要设置成true,保证分页合理化
    interceptor.addInnerInterceptor(pi);
    return interceptor;
}

b 完整的PlusConfig类内容

package com.zlz.config;

import com.baomidou.mybatisplus.annotation.DbType;
import com.baomidou.mybatisplus.extension.plugins.MybatisPlusInterceptor;
import com.baomidou.mybatisplus.extension.plugins.inner.PaginationInnerInterceptor;
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
@MapperScan("com.zlz.mapper")//mapper接口扫描，@MapperScan也可以放在启动类PlusStart上面(启动类也算配置类)
public class PlusConfig {
    @Bean
    public MybatisPlusInterceptor mybatisPlusInterceptor() {
        MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
        //设置分页插件,别的拦截器也是addInnerInterceptor加入进去
        PaginationInnerInterceptor pi = new PaginationInnerInterceptor();
        pi.setDbType(DbType.MYSQL);//设置数据库类型为MySQL
        pi.setOverflow(true);//溢出分页处理,默认是false不处理,需要设置成true,保证分页合理化
        interceptor.addInnerInterceptor(pi);
        return interceptor;
    }
}

c 条件构造器实现分页

c.1 测试代码

@Test
public void findByPage(){
    //创建分页对象
    IPage<Songs> page = new Page<>(1, 5);
    //条件构造器
    QueryWrapper<Songs> qw = new QueryWrapper<>();
    qw.like("name", "天");
    //如果有条件的话,就把条件构造器对象丢到它的第二个形参就是的
    songsService.page(page,qw);
    //输出
    List<Songs> records = page.getRecords();
    for (Songs record : records) {
        System.out.println(record);
    }
    //页码相关
    System.out.println("当前页码:"+page.getCurrent());
    System.out.println("总条数:"+page.getTotal());
    System.out.println("总页数:"+page.getPages());
}

c.1 运行截图

d 自定义sql实现分页

d.1 在SongsMapper接口里面写上自定义方法

 List<Songs> find(IPage<Songs> page, String album);

d.2 在SongsMapper.xml里面写自定义sql语句

 <select id="find" resultType="songs">
        SELECT * FROM songs WHERE album like #{album}
 select>

d.3 测试代码

//自定义分页,要注入自己的mapper
@Autowired
SongsMapper songsMapper;
@Test
public void findByCustomPage(){
    //创建分页对象
    IPage<Songs> page = new Page<>(1, 5);
    String search="年";
    List<Songs> songs = songsMapper.find(page, "%" + search + "%");
    System.out.println(songs);
    //页码相关
    System.out.println("当前页码:"+page.getCurrent());
    System.out.println("总条数:"+page.getTotal());
    System.out.println("总页数:"+page.getPages());
}

d.4 运行截图