jandl-taskmanager-app/be/app/Observers/MasterTaskObserver.php

<?php

namespace App\Observers;

use App\Events\MasterTaskEdited;
use App\Models\MasterTask;

class MasterTaskObserver
{
    public function creating(MasterTask $mastertask)
    {
        $mastertask->color = MasterTask::generateMasterTaskColor();
    }

    public function updating(MasterTask $mastertask)
    {
        // to prevent updating created_by field. this field cannot be updated once created.
        $mastertask->created_by = $mastertask->getOriginal('created_by');

        MasterTaskEdited::dispatch($mastertask, $mastertask->getOriginal());

    }
}