Ekapp/skolehjem/app/Http/Controllers/UserEventController.php

<?php

namespace App\Http\Controllers;

use App\UserEvent;
use Illuminate\Http\Request;
use Illuminate\Http\Response;

class UserEventController extends Controller
{


    /**
     * Update the specified resource in storage.
     *
     * @param  \Illuminate\Http\Request  $request
     * @return \Illuminate\Contracts\Foundation\Application|\Illuminate\Contracts\View\Factory|\Illuminate\View\View
     */
    public function create(Request $request)
    {
        // Get written data from events.index
        $data = $request->validate([
            "user_id" => "required|max:255",
            "event_id" => "required|max:255"
        ]);

        // Check the UserEvent table if there is a row that has the user_id AND the event_id
        $getTableInfo = UserEvent::where('user_id', $request->user_id)
                         ->where('event_id', $request->event_id)->get();

        // If the row has both, then go back and show an error - Cause you're not allowed to be on the same event twice.
        if (count($getTableInfo) > 0)
            return redirect()->route("events.index")->with('error#' . $request->event_id, '<p class="text-center">Du har allerede tilmeldt dig denne Aktivitet!</p>');

        // If not, then it keeps going and saves and shows a success message
        $UserEvent = new UserEvent($data);
        $UserEvent->save();

        return redirect()->route("events.index")->with('signup#' . $request->event_id, '<p class="text-center">Du er hermed tilmeldt denne aktivitet!</p>');
    }
}