Laravel 雄辩地如何通过追加数组中的访问器对集合进行排序
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/25975542/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Laravel eloquent how to order collection by accessor in appends array
提问by gurkov
I have following Eloquent model:
我有以下 Eloquent 模型：
class Song extends Eloquent {
protected $table = 'mg_songs';
protected $hidden = array('events');
protected $appends = array('lastDate');
public function events()
{
return $this->belongsToMany('Event', 'song_event');
}
public function getLastDateAttribute()
{
if (!$this->events) return null;
return $this->events[0]->date->formatLocalized('%d.%m.%Y (%a, %Hч)');
}}
Is it possible to sort by "lastdate" field same as db field:
是否可以按与 db 字段相同的“lastdate”字段进行排序：
$songs->orderBy('title', 'asc'); - works
$songs->orderBy('lastDate', 'desc'); - doesn't works
May be exist simple answer?
可能存在简单的答案？
EDITED:
编辑：
My db structure (only needed fields), with many-to-many:
我的数据库结构（只需要字段），多对多：
events table
event_id
date
事件表
event_id
日期
songs table
song_id
title
歌曲表
song_id
标题
song_event pivot table
id
song_id
event_id
song_event 数据透视表
id
song_id
event_id
SQL-request:
SQL 请求：
SELECT s.title, (SELECT MAX(e.date) FROM events e JOIN song_event se ON (e.id = se.event_id) WHERE se.song_id = s.id) AS s_date FROM mg_songs s ORDER BY s_date desc
回答by Jarek Tkaczyk
You can sort the resulting collection by accessor, obviously the query can't be ordered, for it's not in the db.
您可以通过访问器对结果集合进行排序，显然查询无法排序，因为它不在数据库中。
$songs = Song::all(); // get the result
$songs->sortByDesc('lastDate'); // sort using collection method
// or ascending:
$songs->sortBy('lastDate');
You could achieve the same using joins, if you prefer to do this in the db call (it's better in terms of performance).
joins如果您更喜欢在 db 调用中执行此操作（在性能方面更好），则可以使用 来实现相同的效果。
Another thing: you use if( ! $this->events)which will cause trouble soon.
另一件事：你使用if( ! $this->events)它很快就会引起麻烦。
Check this out:
看一下这个：
// hasOne / belongsTo / morphTo etc - single relations
$model->relation; // returns related model OR null -> evaluates to false
// BUT for hasMany / belongsToMany etc - multiple results
$model->relation; // always returns a collection, even if empty, evaluates to true
So change this ifto:
所以把它改成if：
public function getLastDateAttribute()
{
if ( ! count($this->events)) return null;
return $this->events[0]->date->formatLocalized('%d.%m.%Y (%a, %Hч)');
}}
