Computed values

Earlier we saw how default values can be set for a data object, sometimes you want to set a default value based on other properties. For example, you might want to set a full_name property based on a first_name and last_name property. You can do this by using a computed property:

use Spatie\LaravelData\Attributes\Computed;

class SongData extends Data
{
    #[Computed]
    public string $full_name;

    public function __construct(
        public string $first_name,
        public string $last_name,
    ) {
        $this->full_name = "{$this->first_name} {$this->last_name}";
    }
}

You can now do the following:

SongData::from(['first_name' => 'Ruben', 'last_name' => 'Van Assche']);

Please notice: the computed property won't be reevaluated when its dependencies change. If you want to update a computed property, you'll have to create a new object.

Again there are a few conditions for this approach:

• You must always use a sole property, a property within the constructor definition won't work
• Computed properties cannot be defined in the payload, a CannotSetComputedValue will be thrown if this is the case
• If the ignore_exception_when_trying_to_set_computed_property_value configuration option is set to true, the computed property will be silently ignored when trying to set it in the payload and no CannotSetComputedValue exception will be thrown.