問題描述

我有一個模型列表，它通過它的belongsTo('Model') 關系繼承應該本質上屬于其對應模型所屬的制造商.

I have a model Listing that inherits through its belongsTo('Model') relationship should inherently belong to the Manufacturer that its corresponding Model belongs to.

這是我的列表模型:

    public function model()
    {
        return $this->belongsTo('Model', 'model_id');
    }

    public function manufacturer()
    {
        return $this->belongsTo('Manufacturer', 'models.manufacturer_id');
        /*
        $manufacturer_id = $this->model->manufacturer_id;
        return Manufacturer::find($manufacturer_id)->name;*/
    }

和我的制造商模型:

public function listings()
{
    return $this->hasManyThrough('Listing', 'Model', 'manufacturer_id', 'model_id');
}

public function models()
{
    return $this->hasMany('Model', 'manufacturer_id');
}

我可以在視圖中回顯 $listing->model->name，但不能回顯 $listing->manufacturer->name.這會引發錯誤.我嘗試在 Listing 模型中注釋掉 2 行只是為了獲得效果，然后我可以 echo $listing->manufacturer() 并且這會起作用，但這并不能正確建立它們的關系.我該怎么做呢?謝謝.

I am able to echo $listing->model->name in a view, but not $listing->manufacturer->name. That throws an error. I tried the commented out 2 lines in the Listing model just to get the effect so then I could echo $listing->manufacturer() and that would work, but that doesn't properly establish their relationship. How do I do this? Thanks.

修訂列表模型(感謝回答者):

Revised Listing model (thanks to answerer):

    public function model()
    {
        return $this->belongsTo('Model', 'model_id');
    }

    public function manufacturer()
    {
        return $this->belongsTo('Model', 'model_id')
            ->join('manufacturers', 'manufacturers.id', '=', 'models.manufacturer_id');
    }

推薦答案

我找到了一個解決方案，但不是很簡單.我已經在下面發布了它，但我首先發布了我認為更好的解決方案.

I found a solution, but it's not extremely straight forward. I've posted it below, but I posted what I think is the better solution first.

您不應該直接從列表中訪問制造商，因為制造商僅適用于模型.雖然您可以從列表對象中預先加載制造商關系，但請參見下文.

You shouldn't be able to access manufacturer directly from the listing, since manufacturer applies to the Model only. Though you can eager-load the manufacturer relationships from the listing object, see below.

class Listing extends Eloquent
{
    public function model()
    {
        return $this->belongsTo('Model', 'model_id');
    }
}

class Model extends Eloquent
{
    public function manufacturer()
    {
        return $this->belongsTo('manufacturer');
    }
}

class Manufacturer extends Eloquent
{
} 

$listings = Listing::with('model.manufacturer')->all();
foreach($listings as $listing) {
    echo $listing->model->name . ' by ' . $listing->model->manufacturer->name;
}

為了讓您要求的解決方案發揮作用，我們費了一番周折.解決方案如下:

It took a bit of finagling, to get your requested solution working. The solution looks like this:

public function manufacturer()
{
    $instance = new Manufacturer();
    $instance->setTable('models');
    $query = $instance->newQuery();

    return (new BelongsTo($query, $this, 'model_id', $instance->getKeyName(), 'manufacturer'))
        ->join('manufacturers', 'manufacturers.id', '=', 'models.manufacturer_id')
        ->select(DB::raw('manufacturers.*'));
}

我首先處理查詢并從中構建響應.我希望創建的查詢類似于:

I started off by working with the query and building the response from that. The query I was looking to create was something along the lines of:

SELECT * FROM manufacturers ma
    JOIN models m on m.manufacturer_id = ma.id
WHERE m.id in (?)

通常通過執行 return $this->belongsTo('Manufacturer');

select * from `manufacturers` where `manufacturers`.`id` in (?)

? 將替換為列表表中 manufacturer_id 列的值.此列不存在，因此將插入單個 0，并且您永遠不會返回制造商.

The ? would be replaced by the value of manufacturer_id columns from the listings table. This column doesn't exist, so a single 0 would be inserted and you'd never return a manufacturer.

在我想重新創建的查詢中，我受到了models.id 的約束.通過定義外鍵，我可以在我的關系中輕松訪問該值.于是關系變成了

In the query I wanted to recreate I was constraining by models.id. I could easily access that value in my relationship by defining the foreign key. So the relationship became

return $this->belongsTo('Manufacturer', 'model_id');

這會產生與之前相同的查詢，但會使用 model_ids 填充 ?.所以這會返回結果，但通常是不正確的結果.然后我打算更改我從中選擇的基表.這個值是從模型派生出來的，所以我把傳入的模型改成了Model.

This produces the same query as it did before, but populates the ? with the model_ids. So this returns results, but generally incorrect results. Then I aimed to change the base table that I was selecting from. This value is derived from the model, so I changed the passed in model to Model.

return $this->belongsTo('Model', 'model_id');

我們現在已經模擬了模型關系，太好了，我真的什么都沒有.但至少現在，我可以連接到制造商表.所以我再次更新了關系:

We've now mimic the model relationship, so that's great I hadn't really got anywhere. But at least now, I could make the join to the manufacturers table. So again I updated the relationship:

return $this->belongsTo('Model', 'model_id')
    ->join('manufacturers', 'manufacturers.id', '=', 'models.manufacturer_id');

這讓我們更近了一步，生成了以下查詢:

This got us one step closer, generating the following query:

select * from `models` 
    inner join `manufacturers` on `manufacturers`.`id` = `models`.`manufacturer_id`
    where `models`.`id` in (?)

從這里開始，我想將查詢的列限制為制造商列，為此我添加了選擇規范.這使關系變為:

From here, I wanted to limit the columns I was querying for to just the manufacturer columns, to do this I added the select specification. This brought the relationship to:

返回 $this->belongsTo('Model', 'model_id')->加入('制造商'，'manufacturers.id'，'='，'models.manufacturer_id')->select(DB::raw('manufacturers.*'));

return $this->belongsTo('Model', 'model_id') ->join('manufacturers', 'manufacturers.id', '=', 'models.manufacturer_id') ->select(DB::raw('manufacturers.*'));

并得到查詢

select manufacturers.* from `models` 
    inner join `manufacturers` on `manufacturers`.`id` = `models`.`manufacturer_id`
    where `models`.`id` in (?)

現在我們有一個 100% 有效的查詢，但是從關系返回的對象屬于 Model 類型而不是 Manufacturer.這就是最后一點詭計出現的地方.我需要返回一個 Manufacturer，但希望它受到 where 子句中的models表的約束.我創建了一個新的制造商實例并將表設置為models`并手動創建關系.

Now we have a 100% valid query, but the objects being returned from the relationship are of type Model not Manufacturer. And that's where the last bit of trickery came in. I needed to return a Manufacturer, but wanted it to constrain by themodelstable in the where clause. I created a new instance of Manufacturer and set the table tomodels` and manually create the relationship.

需要注意的是，保存將不起作用.

$listing = Listing::find(1);
$listing->manufacturer()->associate(Manufacturer::create([]));
$listing->save();

這將創建一個新的制造商，然后將 listings.model_id 更新為新制造商的 ID.

This will create a new Manufacturer and then update listings.model_id to the new manufacturer's id.

這篇關于如何在 Laravel 中設置 Eloquent 關系屬于通過另一個模型?的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！