autocde2.0/app/Observers/RequirementObserver.php

<?php

namespace App\Observers;

use App\Models\Requirement;

class RequirementObserver
{
    /**
     * Handle the Requirement "created" event.
     */
    public function created(Requirement $requirement): void
    {
        //
    }

    /**
     * Handle the Requirement "updated" event.
     */
    public function updated(Requirement $requirement): void
    {
        //
    }

    /**
     * Handle the Requirement "deleted" event.
     */
    public function deleted(Requirement $requirement): void
    {
        //

    }

    public function deleting(Requirement $requirement): void
    {
        //
        $requirement->projects()->detach();
        $requirement->tasks()->update(['requirement_id'=>null]);
    }

    /**
     * Handle the Requirement "restored" event.
     */
    public function restored(Requirement $requirement): void
    {
        //
    }

    /**
     * Handle the Requirement "force deleted" event.
     */
    public function forceDeleted(Requirement $requirement): void
    {
        //
    }
}