Laravel - Eager Loading Polymorphic Relation's Related Models

Question

I can eager load polymorphic relations/models without any n+1 issues. However, if I try to access a model related to the polymorphic model, the n+1 problem appears and I can't seem to find a fix. Here is the exact setup to see it locally:

1) DB table name/data

history

companies

products

services

2) Models

// 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) Routing

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

4) Template with n+1 logged only becacuse of $history->historable->company->name, comment it out, n+1 goes away.. but we need that distant related company name:

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

I need to be able to load the company names eagerly (in a single query) as it's a related model of the polymorphic relation models Product and Service. I’ve been working on this for days but can't find a solution. History::with('historable.company')->get() just ignores the company in historable.company. What would an efficient solution to this problem be?

Answer 1

Solution:

It is possible, if you add:

protected $with = ['company'];  

to both the Service and Product models. That way, the company relation is eager-loaded every time a Service or a Product is loaded, including when loaded via the polymorphic relation with History.

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Explanation:

This will result in an additional 2 queries, one for Service and one for Product, i.e. one query for each historable_type. So your total number of queries—regardless of the number of results n—goes from m+1 (without eager-loading the distant company relation) to (m*2)+1, where m is the number of models linked by your polymorphic relation.

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Optional:

The downside of this approach is that you will always eager-load the company relation on the Service and Product models. This may or may not be an issue, depending on the nature of your data. If this is a problem, you could use this trick to automatically eager-load company only when calling the polymorphic relation.

Add this to your History model:

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

Now, when you load the historable polymorphic relation, Eloquent will look for the classes ServiceWithCompany and ProductWithCompany, rather than Service or Product. Then, create those classes, and set with inside them:

ProductWithCompany.php

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

ServiceWithCompany.php

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

...and finally, you can remove protected $with = ['company']; from the base Service and Product classes.

A bit hacky, but it should work.

Answer 2

You can separate the collection, then lazy eager load each one:

$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; 

Probably it's not the best solution, adding protected $with = ['company']; as suggested by @damiani is as good solution, but it depends on your business logic.