Laravel按类别ID分类的最新新闻

问题描述

我正在尝试按类别ID归纳最新新闻。

示例数据：

+----+--------+-------------+-------------------------+-------------------------+
| id | title  | category_id |       created_at        |       updated_at        |
+----+--------+-------------+-------------------------+-------------------------+
|  1 | Item 1 |           1 | 2020-08-01 12:00:00.000 | 2020-08-01 12:00:00.000 |
|  2 | Item 2 |           2 | 2020-08-02 12:00:00.000 | 2020-08-02 12:00:00.000 |
|  3 | Item 3 |           4 | 2020-08-02 12:00:00.000 | 2020-08-02 12:00:00.000 |
|  4 | Item 4 |           1 | 2020-08-04 12:00:00.000 | 2020-08-04 12:00:00.000 |
|  5 | Item 5 |           2 | 2020-08-11 12:00:00.000 | 2020-08-11 12:00:00.000 |
+----+--------+-------------+-------------------------+-------------------------+

我想要输出：

+----+--------+-------------+-------------------------+-------------------------+
| id | title  | category_id |       created_at        |       updated_at        |
+----+--------+-------------+-------------------------+-------------------------+
|  3 | Item 3 |           4 | 2020-08-02 12:00:00.000 | 2020-08-02 12:00:00.000 |
|  4 | Item 4 |           1 | 2020-08-04 12:00:00.000 | 2020-08-04 12:00:00.000 |
|  5 | Item 5 |           2 | 2020-08-11 12:00:00.000 | 2020-08-11 12:00:00.000 |
+----+--------+-------------+-------------------------+-------------------------+

使用Laravel Eloquent是否有一种简便的方法？

解决方法

您将需要自动加入新闻列表，以选择每个类别的最新新闻，例如

select n.*
from news n
left join news n1 on n.category_id = n1.category_id
and n.created_at < n1.created_at
where n1.category_id is null

DEMO

使用查询生成器，您可以将其重写为

DB::table('news as n')
  ->select('n.*')
  ->leftJoin('news as n1',function ($join) {
        $join->on('n.category_id','=','n1.category_id')
             ->whereRaw(DB::raw('n.created_at < n1.created_at'));
   })
  ->whereNull('n1.category_id')
  ->get();