how to store unique values in sessions using laravel?

i want to store unique tasks in sessions of a related job. i am doing like this. Its storing tasks in sessions but not with unique validation. i am also using ajax but i think there is not relation of ajax to store unique value in session.

     $this->validate($request,
            [
                'job_task' => ['required' , 'unique:jobtasks,task_type'],

            ]
        );

        Session::push('jobtasks', $request->all());
        return view('admin.jobs.inc._taskTable');

This the image what i am doing

via Chebli Mohamed