如何在 Laravel 中设置 Eloquent 关系属于通过另一个模型?

问题描述

我有一个模型列表，它通过它的belongsTo('Model') 关系继承应该本质上属于其对应模型所属的制造商.

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

这是我的列表模型:

    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');
}

我可以在视图中回显 $listing->model->name，但不能回显 $listing->manufacturer->name.这会引发错误.我尝试在 Listing 模型中注释掉 2 行只是为了获得效果，然后我可以 echo $listing->manufacturer() 并且这会起作用，但这并不能正确建立它们的关系.我该怎么做呢?谢谢.

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.

修订列表模型(感谢回答者):

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');
    }

推荐答案

我找到了一个解决方案，但不是很简单.我已经在下面发布了它，但我首先发布了我认为更好的解决方案.

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.

您不应该直接从列表中访问制造商，因为制造商仅适用于模型.虽然您可以从列表对象中预先加载制造商关系，但请参见下文.

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;
}

为了让您要求的解决方案发挥作用，我们费了一番周折.解决方案如下:

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.*'));
}

我首先处理查询并从中构建响应.我希望创建的查询类似于:

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 (?)

通常通过执行 return $this->belongsTo('Manufacturer');

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

? 将替换为列表表中 manufacturer_id 列的值.此列不存在，因此将插入单个 0，并且您永远不会返回制造商.

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.

在我想重新创建的查询中，我受到了models.id 的约束.通过定义外键，我可以在我的关系中轻松访问该值.于是关系变成了

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');

这会产生与之前相同的查询，但会使用 model_ids 填充 ?.所以这会返回结果，但通常是不正确的结果.然后我打算更改我从中选择的基表.这个值是从模型派生出来的，所以我把传入的模型改成了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');

我们现在已经模拟了模型关系，太好了，我真的什么都没有.但至少现在，我可以连接到制造商表.所以我再次更新了关系:

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');

这让我们更近了一步，生成了以下查询:

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 (?)

从这里开始，我想将查询的列限制为制造商列，为此我添加了选择规范.这使关系变为:

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.*'));

并得到查询

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

现在我们有一个 100% 有效的查询，但是从关系返回的对象属于 Model 类型而不是 Manufacturer.这就是最后一点诡计出现的地方.我需要返回一个 Manufacturer，但希望它受到 where 子句中的models表的约束.我创建了一个新的制造商实例并将表设置为models`并手动创建关系.

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，保存将不起作用.

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

这将创建一个新的制造商，然后将 listings.model_id 更新为新制造商的 ID.

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

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