一对多的关系计数 - 访问关系的差异 [英] One to many relationship count - difference in accessing relationship

问题描述

我有一对多的关系 - 条目可以有很多访问。

I have one to many relation - Entry can have many Visits.

在我的条目模型中我有以下方法：

In my Entry model I have the following methods:

public function visits() {
    return $this->hasMany ('Visit', 'entry_id','id');
}

public function visitsCount() {
    return $this->hasMany('Visit', 'entry_id','id')
        ->selectRaw('SUM(number) as count')
        ->groupBy('entry_id');
}

在刀片中，我可以使用以下方式获取访问次数：

In Blade I can get number of visits for my entry using:

{{$entry->visits()->count() }}

或

{{ $entry->visitsCount()->first()->count }}

如果我要创建访问器获取访问次数可以定义：

If I want to create accessor for getting number of visits I can define:

public function getNrVisitsAttribute() 
{
    $related = $this->visitsCount()->first();
    return ($related) ? $related->count : 0;
}

现在我可以使用：

{{ $entry->nr_visits }}

问题

Questions:

1. 在一些例子中，我看到了这样定义这种关系： p>
   
   

1. In some examples I saw defining such relation this way:

public function getNrVisitsAttribute()
{    
    if (!array_key_exists('visitsCount', $this->relations)) {
        $this->load('visitsCount');
    }
    $related = $this->getRelation('visitsCount')->first();
    return ($related) ? $related->count : 0;
}

问题是：这与我所展示的简单方法有什么区别？在开始？它是更快/使用更少的资源还是...？

Question is: what's the difference between this and the "simple method" I showed at the beginning? Is it quicker/use less resource or ... ?

为什么这种方法在这种情况下不起作用？ $相关是 null 所以访问者返回 0 而使用简单的方法它返回正确的访问次数

Why this method doesn't work in this case? $related is null so accessor return 0 whereas using "simple method" it returns correct number of visits

我也尝试在 visitsCount 方法关系从 hasMany 到 hasOne ，但不会改变任何内容。 >

I've tried also changing in visitsCount method relationship from hasMany to hasOne but it doesn't change anything.

推荐答案

1您的关系不起作用，因为您没有选择外国人关键：

1 Your relation won't work because you didn't select the foreign key:

public function visitsCount() {
    // also use hasOne here
    return $this->hasOne('Visit', 'entry_id','id')
        ->selectRaw('entry_id, SUM(number) as count')
        ->groupBy('entry_id');
}

2您的访问者应该具有与关系相同的名称，以使其有意义（这就是为什么我首先创建了这些访问器）：

2 Your accessor should have the same name as the relation in order to make sense (that's why I created those accessors in the first place):

public function getVisitsCountAttribute() 
{
   if ( ! array_key_exists('visitsCount', $this->relations)) $this->load('visitsCount');

   $related = $this->getRelation('visitsCount');

   return ($related) ? $related->count : 0;
}

这个访问器只是一种方便的方法来调用count： p>

This accessor is just a handy way to call the count this way:

$entry->visitsCount;

而不是

$entry->visitsCount->count;
// or in your case with hasMany
$entry->visitsCount->first()->count;

所以与性能无关。

还要注意，它不是以不同的方式定义关系，它需要如上所述定义关系。

Also mind that it is not defining the relation differently, it requires the relation to be defined like above.

这篇关于一对多的关系计数 - 访问关系的差异的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！