Aliasing polymorphic types in Laravel's Eloquent
When working with polymorphic relationships in Laravel’s Eloquent, it’s important to specify the “type” of the related model. You can do this by using morphOne, morphMany, and morphToMany methods.
Let’s say we have Book and Author models which shares a polymorphic relationship with Rating model. And the table structure of all these would look like following.
books
id - integer
name - string
authors
id - integer
name - string
ratings
id - integer
url - string
ratingable_id - integer
ratingable_type - string
Here, as you might know, the ratingable_type column of the ratings table detrmines which “type” of parent model to return when accessing the ratingable relation.
So, for instance, if you want to specify this into the Book model, you can do it using morphOne method like so.
<?php
namespace App\Models;
use Illuminate\Database\Eloquent\Model;
class Rating extends Model
{
/**
* Get the parent ratingable model (book or author).
*/
public function ratingable()
{
return $this->morphTo();
}
}
class Book extends Model
{
/**
* Get the book's rating.
*/
public function rating()
{
return $this->morphOne(Rating::class, 'ratingable');
}
}
Now, as you can see, we specified the “type” in the morphOne as the fully qualified class name (FQCN) of the model. But, we can do this the better way using something called “map morphing”.
Aliasing Polymorphich Types
There’s this another way in which you can “map” these FQCNs to strings using Illuminate\Database\Eloquent\Relations\Relation’s morphMap method. You can register this in the boot method of your App\Providers\AppServiceProvider class.
So, if you want to map/alias the App\Models\Rating to rating string, you can do it like so.
<?php
namespace App\Providers;
use Illuminate\Support\ServiceProvider;
use Illuminate\Database\Eloquent\Relations\Relation;
class AppServiceProvider extends ServiceProvider
{
public function boot()
{
Relation::morphMap([
'rating' => 'App\Models\Rating',
]);
}
}
And now you can specify rating as the polymorphic type instead of giving the FQCN like so.
class Book extends Model
{
/**
* Get the book's rating.
*/
public function rating()
{
return $this->morphOne('rating', 'ratingable');
}
}
Benefits of using aliasing types
The main benefit of aliasing polymorphic type is…
- You get a central place where you can manage your polymorphic types.
- As you are aliasing models as strings from a central place, it’s now safe for you to rename the models. By doing so, you don’t have to go over places just to rename the classes.
Caution when using “map morph”
It’s important to note here that, when you start using “map morph” in your existing application, every morphable *_type (ratingable_type in our example) column value in your database that still contains a fully-qualified class will need to be converted to its “map” name.
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