分页管理——基于vue+springboot+mybatis

说在前面：本文只是讲解整体逻辑思路，只有核心代码，作为学习参考笔记

所谓分页，就是把从数据库查出来的数据，按照一定的显示规则显示出来，如下图所示

这个看起来好高端，感觉很难的技术是怎么实现的呢？一般分页技术都是这有这些关键信息：每页显示多少条数据(size)；当前是第几页(current)；一共有多少页(pages)，查询出来的总数据的条数(total)如下图所示

这些数据从后台传到前端显示，我们来根据浏览器的开发者工具下的Network下page文件中response preview下来看看传输来数据格式

显然，这些数据都是封装好了的，那么后端是如何封装传输的呢？

首先有个核心，就是基于Mybatis-plus下的Page类，Mybatis-plus已经帮我们封装好了这个Page类，来我们先看看这个Page类，显然它还继承了一个Pagination类

//Page类
package com.baomidou.mybatisplus.plugins;
import com.baomidou.mybatisplus.plugins.pagination.Pagination;
...

public class Page<T> extends Pagination {
    private static final long serialVersionUID = 1L;
    private List<T> records = Collections.emptyList();
    private Map<String, Object> condition;
	··· 
}

//Pagination类
package com.baomidou.mybatisplus.plugins.pagination;
...
public class Pagination extends RowBounds implements Serializable {
    private static final long serialVersionUID = 1L;
    private int total;
    private int size;
    private int pages;
    private int current;
    private boolean searchCount;
    private boolean openSort;
    private String orderByField;
    private boolean isAsc;
    ···
}

接下来看看dto层、Mapper层、Service层、Controller层是怎么实现的

//Controller层
	public ApiResult page(@RequestBody DictQueryInput query) {
        Page<DictListItem> page = new Page<>();
        page.setSize(query.getLimit());
        page.setCurrent(query.getPage());
        dictService.listPage(page, query);
        return ApiResult.ok("获取数据字典分页列表成功", page);
        ···
    }

//dto层
	public class DictListItem {

    private String dictKey;

    private String dictValue;

    private String parentKey;

    private String status;

    private String remark;

    private Integer dictId;
        
    private Integer parentId;

    private boolean selected = false;
    ···
    }

public class DictQueryInput extends BasePageQuery {

    private Integer dictId;

    private String code;

    private String value;
    ···
}

public class BasePageQuery {

    @ApiModelProperty(value = "当前页", required = true, position = 0)
    private Integer page;

    @ApiModelProperty(value = "每页显示数量", required = true, position = 1)
    private Integer limit;
    ···
}

//Service层
public interface IDictService extends IService<Dict> {

    /**
     * 列表分页
     */
    Page<DictListItem> listPage(Page<DictListItem> page, DictQueryInput filter);
    ...
}

//Service层实现类
@Service
public class DictServiceImpl extends ServiceImpl<DictMapper, Dict> implements IDictService {

    @Autowired
    DictMapper dictMapper;

    @Override
    public Page<DictListItem> listPage(Page<DictListItem> page, DictQueryInput filter) {
        page.setRecords(dictMapper.listPage(page, filter));
        return page;
    
        ...
    }

这里有一个很关键的语句page.setRecords(dictMapper.listPage(page, filter));这表示了把查出来的数据封装到了Page类下的records中，以List的形式，如下图所示

//Mapper层
public interface DictMapper extends BaseMapper<Dict> {

    /**
     * 检索数据字典分页
     */
    List<DictListItem> listPage(Pagination page, @Param("filter") DictQueryInput filter);
    ...
}

<mapper namespace="com.orisdom.modules.basic.mapper.DictMapper">
   <resultMap id="DictListItem" type="com.orisdom.modules.basic.dto.output.DictListItem">
        <id column="dict_id" property="dictId"/>
        <result column="dict_key" property="dictKey"/>
        <result column="dict_value" property="dictValue"/>
        <result column="parent_id" property="parentId"/>
        <result column="status" property="status"/>
        <result column="parent_key" property="parentKey"/>
    resultMap>
    
    <select id="listPage" resultMap="DictListItem">
        SELECT
            d.*, dd.dict_key AS 'parent_key'
        FROM
            bs_dict d
        LEFT JOIN bs_dict dd ON (d.parent_id = dd.dict_id)
        WHERE
            1 = 1
        <if test="filter.code!=null and filter.code!=''">
            AND d.`code` = #{filter.code}
        if>
        ORDER BY d.display_order_no, d.display_order ASC
    select>

---

结语

善于利用Mybatis-plus工具，的确很神奇，但是必须要先结合一个项目学习如何使用，官方介绍的反正我是没有看懂的。。。大家还有不明白的欢迎留言哦~