Ideas/app/Http/Controllers/CommentController.php

<?php

namespace App\Http\Controllers;

use App\Models\Comment;
use App\Models\Idea;
use Illuminate\Http\Request;

class CommentController extends Controller
{
    public function store(Idea $idea)
    {
        $comment = new Comment();
        $comment->idea_id = $idea->id;
        $comment->content = \request()->get("content");
        $comment->save();

        return redirect()->route("ideas.show", $idea->id)->with("success", "Comment created successfully");
    }
}