Laravel 中关系的计数关系

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('AppQuestion','conversation_id','conversation_id');
    }
    public function category ()
    {
        return $this->belongsTo('AppCategory', 'cat', 'cat_id');
    }

}

还有一个像这样的 Question 模型:

And a Question model like this:

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

如您所见，这两者之间存在 hasMany 关系.

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

另一方面，有一个像下面这样的 Category 与 Conversation 模型有关系:

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('AppConversation','cat','cat_id');
    }
}

现在我想将一个名为 question_count 的属性附加到 Category 来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: IlluminateDatabaseEloquentCollection::$questions

我做了什么?如何在最小服务器过载的情况下计算关系的关系?

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

我使用的是 Laravel 5.3.4.

I am using laravel 5.3.4.

推荐答案

我认为这里你需要一个有很多的关系.

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

你做错了什么:

当你写$this->conversations->questions时，这是行不通的，因为questions是单个对话的关系 而不是对话的集合(这里，$this->conversations 是一个集合)

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)

解决办法:

使用 hasManyThrough 关系:

Using hasManyThrough relation:

您可以在在此页面上找到有关此关系的文档，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，你需要在你的 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('AppConversation');
    }

    public function questions ()
    {
        return $this->hasManyThrough('AppQuestion', 'AppConversation');
    }
}

(我会让你查看非标准外键的文档)

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

然后你应该可以使用:$category->questions->count()

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