在laravel中计算关系的关系 [英] count relation of relation in laravel

问题描述

假设我有一个像这样的Conversation模型:

Suppose I have a Conversation model like this :

class Conversation extends Model
{
    public function questions (){
        return $this->hasMany('App\Question','conversation_id','conversation_id');
    }
    public function category ()
    {
        return $this->belongsTo('App\Category', 'cat', 'cat_id');
    }

}

和这样的Question模型:

class Question extends Model
{
    public function conversation ()
    {
        return $this->belongsTo('App\Conversation', 'conversation_id', 'conversation_id');
    }
}

如您所见，这两者之间存在一个hasMany关系.

As you can see there is a hasMany relation between those two.

另一方面，如下所示的Category与Conversation模型有关:

In the other hand there is a Category like below that has a relation with Conversation model :

class Category extends Node
{
    public function conversations (){
        return $this->hasMany('App\Conversation','cat','cat_id');
    }
}

现在，我想向Category附加一个名为question_count的属性，该属性计算每个类别的对话的所有问题.为此，我添加了这个:

Now I want to append an attribute named question_count to Category that counts all questions of conversations of each category. for that I added this :

    public function getQuestionsCountAttribute ()
    {
        return $this->conversations->questions->count();
    }

但是在获取类别时，出现此错误:

But when fetch a category I got this error :

ErrorException in Category.php line 59:
Undefined property: Illuminate\Database\Eloquent\Collection::$questions

我做了什么?如何计算具有最小服务器超载的关系的关系?

What did I do? how can I count relations of a relation with minimum server overloading?

我正在使用laravel 5.3.4.

I am using laravel 5.3.4.

推荐答案

我认为您需要在这里拥有很多直通关系.

I think that you need a has many through relationship here.

您在做什么:

编写$this->conversations->questions时，此操作不起作用，因为questions是单个对话的关系，而不是对话集合的关系(此处，$this->conversations是集合)

When you write $this->conversations->questions, this can't work, because the questions are a relation of a single conversation and not of a collection of conversations (here, $this->conversations is a Collection)

解决方案:

使用hasManyThrough关系:

Using hasManyThrough relation:

您可以在此页面上上找到该文档，如果我的解释不好

You can find the documentation for this relation on this page, if my explanation is bad

基础是，您需要在Category模型上定义一个关系:

The basics are, you need to define a relation on your Category model:

class Category extends Node
{
    public function conversations ()
    {
        return $this->hasMany('App\Conversation');
    }

    public function questions ()
    {
        return $this->hasManyThrough('App\Question', 'App\Conversation');
    }
}

(我会让您查看非标准外键的文档)

(I will let your look into the documentation for your non standards foreign keys)

然后您应该可以使用:$category->questions->count()

You should then be able to use: $category->questions->count()

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