通用Mapper和PageHelper入门

两个项目的共同点都是mybatis的插件,并且出自同一作者之手

通用Mapper介绍:

1. 可以方便完成单表的增删改查,暂不支持多表的查询
2. 抛弃mapper.xml的编写, 对于频繁修改数据库的情况,只需修改 model中的字段即可
3. 当不同数据库进行切换的时候,无需修改代码
4. 应用的缓存机制,并不是每次都是动态生成sql语句

pageHelpr介绍

无感知完成分页过程,利用Threadlocal完成完成Page对象在线程间的传输.

• springboot 集成
  pom.xml

<dependency>
	<groupId>mysql</groupId>
	<artifactId>mysql-connector-java</artifactId>
</dependency>
<!--通用mapper中已经添加了mybatis的启动器的依赖因此可以省略-->
<dependency>
    <groupId>tk.mybatis</groupId>
    <artifactId>mapper-spring-boot-starter</artifactId>
</dependency>

<dependency>
    <groupId>com.github.pagehelper</groupId>
    <artifactId>pagehelper-spring-boot-starter</artifactId>
</dependency>

application.yaml配置

spring:
  datasource:
    driver-class-name: com.mysql.jdbc.Driver
    url: jdbc:mysql://192.168.2.156:3306/heima
    username: root
    password: 123456
mybatis:
  type-aliases-package: com.leyou.item.pojo

springboot启动类

import tk.mybatis.spring.annotation.MapperScan;

@EnableDiscoveryClient
@SpringBootApplication
//此处一定要引用通用mapper的依赖
@MapperScan("com.leyou.mapper")
public class LeyouItemServiceApp {
    public static void main(String[] args) {
        SpringApplication.run(LeyouItemServiceApp.class,args);
    }
}

mapper.java文件和javabean

package com.leyou.mapper;
import com.leyou.item.pojo.Brand;
import tk.mybatis.mapper.common.Mapper;

public interface BrandMapper extends Mapper<Brand> {
}
//javabean
@Table(name = "tb_brand")
@Data
public class Brand {
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    private Long id;
    private String name;
    private String image;
    private Character letter;
}

代码中的应用

public List<Category> queryCategoryByPid(Long pid) {
     Category category = new Category();
     //通过对象中的属性查询列表数据
     category.setParentId(pid);
     return categoryMapper.select(category);
 }

    public PageResult<Brand> queryBrandsByPage(String key, Integer page, Integer rows, String sortBy, Boolean desc) {
        //建立查询的example对象
        Example example = new Example(Brand.class);
        //获取查询条件
        Example.Criteria criteria = example.createCriteria();
        //根据属性信息确定查询条件
        if(StringUtils.isNotBlank(key)){
            //模糊查询的确定方式
            criteria.andLike("name","%"+key+"%").orEqualTo("letter",key);
        }

        if(StringUtils.isNotBlank(sortBy)){
            //排序操作
            example.setOrderByClause(sortBy+" "+(desc?"desc":"asc"));
        }
        //通用PageHelper用法一
        PageHelper.startPage(page,rows);
        //我感觉侵犯你,总条数,分页语句已经执行,
        List<Brand> brands = brandMapper.selectByExample(example);
        //将分页数据解析
        PageInfo<Brand> info = new PageInfo<>(brands);
        return new PageResult<>(info.getTotal(),info.getList());
    }