Solution 1 :using if

           $posts = Post::select("*");

  

            if ($request->has('user_id')) {

                $posts = $posts->where('user_id', $request->user_id);

            }



            $posts = $posts->get();
                

Solution 2 : using when() (Better solution)

                $posts = Post::select("*")
                    ->when($request->has('user_id'), function ($query) use ($request) {
                        $query->where('user_id', $request->user_id);
                    })
                    ->get();
  
                 dd($posts);

                

If else

                $posts = Post::select("*");

  

if ($request->get('order_by') == "publish_date") {

    $posts = $posts->orderBy('publish_date', 'desc');

} else {

    $posts = $posts->orderBy('created_at', 'desc');

}



$posts = $posts->get();

Using when()

$posts = Post::select("*")
                    ->when($request->get('order_by') == "publish_date", function ($query) {
                            return $query->orderBy('publish_date', 'desc');
                        }, function ($query) {
                            return $query->orderBy('created_at', 'desc');
                        })
                        ->get();
   
        dd($posts);

                    

Multiple When()

                    public function index(Request $request)
    {
        $posts = Post::select("*")
                    ->when($request->has('user_id'), function ($query) use ($request) {
                        $query->where('user_id', $request->user_id);
                    })
                    ->when($request->has('category_id'), function ($query) use ($request) {
                        $query->where('category_id', $request->category_id);
                    })
                    ->when($request->has('title'), function ($query) use ($request) {
                        $query->where('title', 'LIKE', '%' . $request->title .'%');
                    })
                    ->get();
   
        dd($posts);
    }