로드 시 Laravel/Eloquent 모델에 사용자 정의 속성을 추가하는 방법은 무엇입니까?

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

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

<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>

<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>