Check if relation exists

ImagesController.php

<?php

namespace App\Http\Controllers\Api;

use App\Image;
use App\Article;
use App\Http\Requests;
use Illuminate\Http\Request;
use App\Transformers\ImageTransformer;
use App\Http\Controllers\Api\ApiController;

class ImagesController extends ApiController
{
    protected $imageRelation = [
        'articles' => '\App\Article',
        'contacts' => '\App\Contact'
    ];
    
    public function index(Request $request)
    {
        $eagerLoad = $this->eagerLoad($request);
        $paginator = Image::with($eagerLoad)->paginate($this->number);
        
        return $this->respondWithPaginator($paginator, new ImageTransformer);
    }

    public function getRelatedImages(Request $request, $model, $id)
    {
        $name = $this->getModelName($model);
        if (! $name) {
            return $this->errorWrongArgs($model.' has no relation with images');
        }
          
        $resource = $name::where('id', $id)->with('images')->first();
        if (! $resource) {
            return $this->errorNotFound(class_basename($name).' not found');
        }
        
        return $this->respondWithCollection($resource->images, new ImageTransformer);
    }

    protected function getModelName($model)
    {
        if (isset($this->imageRelation[$model])) {
            return (string) $this->imageRelation[$model];
        }
        return false;
    }
}