How to Add a Custom Attribute to a Laravel/Eloquent Model on Load?

Add a Custom Attribute to a Laravel/Eloquent Model on Load

Problem Analysis

In Laravel/Eloquent, custom attributes not directly related to a column in the underlying table are excluded when converting models to toArray() or JSON format.

Solution

Laravel 8 and above:

Use the Attribute class to create a custom accessor that automatically calculates and assigns the attribute when the object loads.

<code class="php">class EventSession extends Eloquent {
  public function availability() {
    return new Attribute(
      get: fn () => $this->calculateAvailability()
    );
  }
}</code>

Laravel 7 and below:

Option 1: Append Attribute to $appends Property

Add the custom attribute to the $appends array and define an appropriate accessor.

<code class="php">class EventSession extends Eloquent {
  protected $appends = ['availability'];
  public function getAvailabilityAttribute() {
    return $this->calculateAvailability();
  }
}</code>

Option 2: Override toArray() Method

Override the toArray() method and explicitly set or iterate over the custom attributes.

<code class="php">class Book extends Eloquent {
  public function toArray() {
    $array = parent::toArray();
    $array['upper'] = $this->upper;
    return $array;
  }
  public function getUpperAttribute() {
    return strtoupper($this->title);
  }
}</code>

Option 3: Loop Through Mutated Attributes

Loop through the model's mutated attributes and apply them to the toArray() array.

<code class="php">class Book extends Eloquent {
  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);
  }
}</code>

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