Dynamic Eloquent Relation By Macro

One important thing in the modular system is dynamic variability; and most importantly, it’s a change without manipulating the kernel file.

Question :

So, suppose we have a Post model for the blog system, and then we want to add a module to add `categories` to our posts. If we do not have access to the post model file, how can we import the related relation to retrieve and save our categories?

Solution:

To put the categories relationship in our post model, we can use the macro at Laravel Eloquent Builder.

So; put this code at register method of your ServiceProvider:

// at top of your provider
use Illuminate\Database\Eloquent\Builder; 
use App\Category;
// at register method
Builder::macro(‘categories’, function() {
    $model = $this->getModel();
    return $model->belongsToMany(Category::class);
 });

At the end; for ensure that we are using relation in correct model; we should change above code like this:

// at top of your provider
use Illuminate\Database\Eloquent\Builder;
use App\Post;
use App\Category;
// at register method
Builder::macro(‘categories’, function() {
    $model = $this->getModel();
    
    if($model instanceof Post) {
         return $model->belongsToMany(Category::class);
    }
    unset(static::$macros['categories']);
    return $model->categories();
 });