mybatis-plus多表分页查询最佳实现（简单）

1.简介

在Mybatis Plus 中，虽然IService 接口帮我们定义了很多常用的方法，但这些都是 T 对象有用，如果涉及到 多表的查询，还是需要自定义Vo 对象和自己编写sql 语句，Mybatis Plus提供了一个Page 对象,查询是需要设置其中的 size 字段 和 current 字段的值。

mybatis-plus的单表分页就不必多说了，那多表联查的分页该如何实现呢？其实也很简单，你只需要自己写好关联查询的sql再结合mybatis-plus提供的分页对象，就可以实现了。但是如何才能优雅的将分页参数和查询条件提供给mybatis-plus呢？我选择使用
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;这个对象来实现。直接继承baomidou提供的类可以省去每次手动再new对象，因为在获取参数时就已经自动构建了

2.实现

2.1版本

    3.5.1
    8.0.18

            
            
            <dependency>
                <groupId>com.baomidougroupId>
                <artifactId>mybatis-plus-boot-starterartifactId>
                <version>${mybatis-plus.version}version>
            dependency>
            
            <dependency>
                <groupId>com.baomidougroupId>
                <artifactId>mybatis-plus-generatorartifactId>
                <version>${mybatis-plus.version}version>
            dependency>
            
            
            <dependency>
                <groupId>mysqlgroupId>
                <artifactId>mysql-connector-javaartifactId>
                <version>${connector.version}version>
            dependency>

2.2分页插件

@MapperScan(“。。。”)这些基本配置我就不多说了

@Configuration
public class MPConfig {
    /**
     * 分页插件
     */
    @Bean
    public MybatisPlusInterceptor mybatisPlusInterceptor() {
        MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
        //乐观锁
        //interceptor.addInnerInterceptor(new OptimisticLockerInnerInterceptor());
        //分页锁
        interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.MYSQL));
        return interceptor;
    }

}

2.3 分页参数 继承 自 Page

直接继承baomidou提供的类可以省去每次手动再new对象，因为在获取参数时就已经自动构建了

package com.dxf.common.utils;
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import io.swagger.annotations.ApiModelProperty;
import io.swagger.annotations.ApiParam;
import springfox.documentation.annotations.ApiIgnore;
import java.util.List;

public class PageParam<T> extends Page<T> {

    /**
     * 查询数据列表
     */
    @ApiParam(hidden = true)
    private List<T> records;
    /**
     * 总数
     */
    @ApiParam(hidden = true)
    private long total = 0;

    /**
     * 每页显示条数，默认 10
     */
    @ApiParam(value = "每页大小，默认10",required = false, defaultValue = "10")
    private long size = 10;

    /**
     * 当前页
     */
    @ApiParam(value = "当前页，默认1",required = false,defaultValue = "1")
    private long current = 1;

    /**
     * 是否进行 count 查询
     */
    @ApiParam(hidden = true)
    private boolean isSearchCount = true;

    @Override
    @ApiParam(hidden = true)
    public List<T> getRecords() {
        return this.records;
    }

    @Override
    public Page<T> setRecords(List<T> records) {
        this.records = records;
        return this;
    }

    @Override
    public long getTotal() {
        return this.total;
    }

    @Override
    public Page<T> setTotal(long total) {
        this.total = total;
        return this;
    }

    @ApiParam(hidden = true)
    public boolean getSearchCount() {
        if (total < 0) {
            return false;
        }
        return isSearchCount;
    }

    @Override
    @ApiParam(hidden = true)
    public boolean isSearchCount() {
        if (total < 0) {
            return false;
        }
        return isSearchCount;
    }

    @Override
    public Page<T> setSearchCount(boolean isSearchCount) {
        this.isSearchCount = isSearchCount;
        return this;
    }

    @Override
    public long getSize() {
        return this.size;
    }

    @Override
    public Page<T> setSize(long size) {
        this.size = size;
        return this;
    }

    @Override
    public long getCurrent() {
        return this.current;
    }

    @Override
    public Page<T> setCurrent(long current) {
        this.current = current;
        return this;
    }
}

2.4 实现的重点mapper

import org.apache.ibatis.annotations.Param;

public interface SysRoleMapper extends BaseMapper<SysRole> {

    IPage<SysRole> searchPage(PageParam<SysRole> pageParam, @Param("name") String name);
}

关联的是角色表和用户表

DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.dxf.data.mapper.SysRoleMapper">

    <select id="searchPage" resultType="com.dxf.data.entity.SysRole">
        SELECT r.id,r.name,r.status,r.role_sort, a.name create_by ,r.create_time,r.update_time,r.remark
        FROM sys_role r left join sys_user a on r.create_by=a.id
        <where>
            <if test="name != null and name != ''">
                r.name like concat(#{name},'%')
            if>
        where>
        order by r.role_sort
    select>
mapper>

2.5 其他层就是传下参数

@RestController
@RequestMapping("/admin/role")
@Api(tags  = "SysRoleControllr|角色控制器")
public class SysRoleController {
    @Autowired
    SysRoleService roleService;
    
    @GetMapping("/page")
    @ApiOperation("角色列表分页查询")
    public ResultJson page(PageParam<SysRole> pageParam,String likeKey) {
        IPage<SysRole> iPage = roleService.searchPage(pageParam,likeKey);
        Map<String, Object> map = new HashMap<>();
        map.put("rows",iPage.getRecords());
        map.put("total",iPage.getTotal());
        return ResultJson.ok().data(map);
    }
public interface SysRole

}
Service extends IService<SysRole> {

    /**
     * 分页查询角色
     */
    IPage<SysRole> searchPage(PageParam<SysRole> pageParam,String name);
}


@Service
public class SysRoleServiceImpl extends ServiceImpl<SysRoleMapper, SysRole> implements SysRoleService {

    @Override
    public IPage<SysRole> searchPage(PageParam<SysRole> pageParam,String name) {
        return baseMapper.searchPage(pageParam,name);
    }
}