How to Add Custom Attributes to Laravel Eloquent Models on Load?

In Laravel Eloquent, you may encounter a scenario where you want to add a custom attribute to a model when it's loaded. For example, consider a controller like this:

public function index()
{
    $sessions = EventSession::all();
    foreach ($sessions as $i => $session) {
        $sessions[$i]->available = $session->getAvailability();
    }
    return $sessions;
}

It would be convenient to skip the manual loop and have the 'available' attribute populated automatically.

The Problem

The issue here is that the toArray() method of a model ignores accessors that don't correspond to columns in the underlying table. This is an intentional design for performance reasons.

The Solution

Laravel Versions >= 8:

Luckily, there's an elegant way to achieve this using the Attribute class:

class EventSession extends Eloquent {

    protected $table = 'sessions';

    public function availability()
    {
        return new Attribute(
            get: fn () => $this->calculateAvailability()
        );  
    }
}

Laravel Versions

Option 1: Appends Property

For versions less than 8, you can use the $appends property to control which attributes are included in the serialized form of the model:

class EventSession extends Eloquent {

    protected $table = 'sessions';
    protected $appends = array('availability');

    public function getAvailabilityAttribute()
    {
        return $this->calculateAvailability();  
    }
}

Option 2: Override toArray() Method

Alternatively, you can override the toArray() method and manually set the attribute:

class Book extends Eloquent {

    protected $table = 'books';
    
    public function toArray()
    {
        $array = parent::toArray();
        $array['upper'] = $this->upper;
        return $array;
    }
    
    public function getUpperAttribute()
    {
        return strtoupper($this->title);    
    }

}

Option 3: Loop Through Mutated Attributes

If you have numerous custom accessors, you can iterate through them and apply them during serialization:

class Book extends Eloquent {

    protected $table = 'books';
    
    public function toArray()
    {
        $array = parent::toArray();
        foreach ($this->getMutatedAttributes() as $key)
        {
            if ( ! array_key_exists($key, $array)) {
                $array[$key] = $this->{$key};   
            }
        }
        return $array;
    }
    
    public function getUpperAttribute()
    {
        return strtoupper($this->title);    
    }

}