exchange/app/Http/Controllers/Api/DocumentController.php

<?php

namespace App\Http\Controllers\Api;

use App\Models\Document;
use App\Transformers\DocumentTransformer;
use Illuminate\Http\Request;

class DocumentController extends ApiController
{
    public function index(Request $request)
    {
        $page = $request->page ?? null;
        $category = $request->category ?? null;
        if($page){
            $documents = Document::where('page', $page)->orderBy('lft', 'asc');
            if(count($documents->get()) < 1){
                return $this->errorNotFound();
            }
        }else{
            $documents = Document::orderBy('lft', 'asc');
        }
        if($category){
            $documents = $documents->where('document_category_id', $category);
        }
        
        return $this->respondWithCollection($documents->get(), new DocumentTransformer($this->locale));
    }
}