Laravel - 渴望加载多态关系的相关模型

Question

我可以在没有任何n + 1问题的情况下加载多态关系/模型。但是，如果我尝试访问与多态模型相关的模型，则会出现n + 1问题，而我似乎无法找到修复方法。以下是在本地查看的确切设置：

1）数据库表名称/数据

history

    companies

    products

    services

2）模特

// History
class History extends Eloquent {
    protected $table = 'history';

    public function historable(){
        return $this->morphTo();
    }
}

// Company
class Company extends Eloquent {
    protected $table = 'companies';

    // each company has many products
    public function products() {
        return $this->hasMany('Product');
    }

    // each company has many services
    public function services() {
        return $this->hasMany('Service');
    }
}

// Product
class Product extends Eloquent {
    // each product belongs to a company
    public function company() {
        return $this->belongsTo('Company');
    }

    public function history() {
        return $this->morphMany('History', 'historable');
    }
}

// Service
class Service extends Eloquent {
    // each service belongs to a company
    public function company() {
        return $this->belongsTo('Company');
    }

    public function history() {
        return $this->morphMany('History', 'historable');
    }
}

3）路由

Route::get('/history', function(){
    $histories = History::with('historable')->get();
    return View::make('historyTemplate', compact('histories'));
});

4）n + 1模板仅因为$ history-＆gt; historable-＆gt; company-＆gt;名称而被记录，注释掉，n + 1消失..但我们需要那个遥远的相关公司名：

@foreach($histories as $history)
    <p>
        <u>{{ $history->historable->company->name }}</u>
        {{ $history->historable->name }}: {{ $history->historable->status }}
    </p>
@endforeach
{{ dd(DB::getQueryLog()); }}

我需要能够热切地（在单个查询中）加载公司名称，因为它是多态关系模型Product和Service的相关模型。 我已经做了好几天了，但找不到解决办法。 History::with('historable.company')->get()只会忽略company中的historable.company。 这个问题的有效解决方案是什么？

Answer 1

<强>解决方案：

如果你添加：

，这是可能的

protected $with = ['company']; 

同时使用Service和Product模型。这样，每次加载company或Service时都会加载Product关系，包括通过与History的多态关系加载时。

---

<强>解释

这会产生额外的2个查询，一个用于Service，另一个用于Product，即每个historable_type一个查询。因此，无论结果数量n如何，您的查询总数都会从m+1（没有急切加载远距离company关系）转到(m*2)+1，其中m 1}}是由多态关系链接的模型数。

---

可选

这种方法的缺点是，总是在company和Service模型上急切加载Product关系。这可能是也可能不是问题，具体取决于数据的性质。如果这是一个问题，您可以使用此技巧在调用多态关系时自动加载company 。

将此添加到您的History型号：

public function getHistorableTypeAttribute($value)
{
    if (is_null($value)) return ($value); 
    return ($value.'WithCompany');
}

现在，当您加载historable多态关系时，Eloquent会查找类ServiceWithCompany和ProductWithCompany，而不是Service或Product。然后，创建这些类，并在其中设置with：

<强> ProductWithCompany.php

class ProductWithCompany extends Product {
    protected $table = 'products';
    protected $with = ['company'];
}

<强> ServiceWithCompany.php

class ServiceWithCompany extends Service {
    protected $table = 'services';
    protected $with = ['company'];
}

...最后，您可以从基础protected $with = ['company'];和Service类中删除Product。

有点hacky，但它应该工作。

Answer 2

你可以分开收集，然后懒得加载每一个：

$histories =  History::with('historable')->get();

$productCollection = new Illuminate\Database\Eloquent\Collection();
$serviceCollection = new Illuminate\Database\Eloquent\Collection();

foreach($histories as $history){
     if($history->historable instanceof Product)
          $productCollection->add($history->historable);
     if($history->historable instanceof Service)
        $serviceCollection->add($history->historable);
}
$productCollection->load('company');
$serviceCollection->load('company');

// then merge the two collection if you like
foreach ($serviceCollection as $service) {
     $productCollection->push($service);
}
$results = $productCollection;

可能这不是最好的解决方案，按照@damiani的建议添加protected $with = ['company'];是一个很好的解决方案，但这取决于你的业务逻辑。

Answer 3

拉取请求#13737和#13741解决了此问题。

只需更新您的Laravel版本和以下代码

即可

protected $with = [‘likeable.owner’];

将按预期工作。

Answer 4

我对此并不是100％肯定，因为在我的系统中重新创建代码很困难，但belongTo('Company')可能应该是morphedByMany('Company')。您也可以尝试morphToMany。我能够获得复杂的多态关系，无需多次调用即可正确加载。 ？

Answer 5

正如JoãoGuilherme所提到的，这在版本5.3中得到了修复。但是，我发现自己在应用程序中面临同样的错误，升级是不可行的。所以我创建了一个覆盖方法，将修复程序应用于Legacy API。 （感谢João，指出我正确的方向来制作它。）

首先，创建您的Override类：     

namespace App\Overrides\Eloquent;

use Illuminate\Database\Eloquent\Relations\MorphTo as BaseMorphTo;

/**
 * Class MorphTo
 * @package App\Overrides\Eloquent
 */
class MorphTo extends BaseMorphTo
{
    /**
     * Laravel < 5.2 polymorphic relationships fail to adopt anything from the relationship except the table. Meaning if
     * the related model specifies a different database connection, or timestamp or deleted_at Constant definitions,
     * they get ignored and the query fails.  This was fixed as of Laravel v5.3.  This override applies that fix.
     *
     * Derived from https://github.com/laravel/framework/pull/13741/files and
     * https://github.com/laravel/framework/pull/13737/files.  And modified to cope with the absence of certain 5.3
     * helper functions.
     *
     * {@inheritdoc}
     */
    protected function getResultsByType($type)
    {
        $model = $this->createModelByType($type);
        $whereBindings = \Illuminate\Support\Arr::get($this->getQuery()->getQuery()->getRawBindings(), 'where', []);
        return $model->newQuery()->withoutGlobalScopes($this->getQuery()->removedScopes())
            ->mergeWheres($this->getQuery()->getQuery()->wheres, $whereBindings)
            ->with($this->getQuery()->getEagerLoads())
            ->whereIn($model->getTable().'.'.$model->getKeyName(), $this->gatherKeysByType($type))->get();
    }
}

接下来，你需要一些能让你的Model类真正与你的MorphTo而不是Eloquent的化身交谈的东西。这可以通过应用于每个模型的特征，或者由模型类而不是Illuminate \ Database \ Eloquent \ Model直接扩展的Illuminate \ Database \ Eloquent \ Model的子项来完成。我选择将其变成一种特质。但是如果你选择让它成为一个儿童班，我就会离开那个推断这个名字作为单挑的部分，这是你需要考虑的事情：

<?php

namespace App\Overrides\Eloquent\Traits;

use Illuminate\Support\Str;
use App\Overrides\Eloquent\MorphTo;

/**
 * Intended for use inside classes that extend Illuminate\Database\Eloquent\Model
 *
 * Class MorphPatch
 * @package App\Overrides\Eloquent\Traits
 */
trait MorphPatch
{
    /**
     * The purpose of this override is just to call on the override for the MorphTo class, which contains a Laravel 5.3
     * fix.  Functionally, this is otherwise identical to the original method.
     *
     * {@inheritdoc}
     */
    public function morphTo($name = null, $type = null, $id = null)
    {
        //parent::morphTo similarly infers the name, but with a now-erroneous assumption of where in the stack to look.
        //So in case this App's version results in calling it, make sure we're explicit about the name here.
        if (is_null($name)) {
            $caller = last(debug_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS, 2));
            $name = Str::snake($caller['function']);
        }

        //If the app using this trait is already at Laravel 5.3 or higher, this override is not necessary.
        if (version_compare(app()::VERSION, '5.3', '>=')) {
            return parent::morphTo($name, $type, $id);
        }

        list($type, $id) = $this->getMorphs($name, $type, $id);

        if (empty($class = $this->$type)) {
            return new MorphTo($this->newQuery(), $this, $id, null, $type, $name);
        }

        $instance = new $this->getActualClassNameForMorph($class);
        return new MorphTo($instance->newQuery(), $this, $id, $instance->getKeyName(), $type, $name);
    }
}