Can I use ORM without connecting entity to a database table

So... am I doing this wrong?

Yes. It doesn't make sense to use the ORM interfaces if you don't really want to use an ORM.

I think the best approach is NOT to think about implementation details at all. Introduce your own interfaces for repositories:

interface Products{    /**     * @param string $slug     *     * @return Product[]     */    public function findBySlug($slug);}interface Orders{    /**     * @param Product $product     *      * @return Order[]     */    public function findProductOrders(Product $product);}

And implement them with either an ORM:

class DoctrineProducts implements Products{    private $em;    public function __construct(EntityManager $em)    {        $this->em = $em;    }    public function findBySlug($slug)    {        return $this->em->createQueryBuilder()           ->select()           // ...    }}

or a Rest client:

class RestOrders implements Orders{    private $httpClient;    public function __construct(HttpClient $httpClient)    {        $this->httpClient = $httpClient;    }    public function findProductOrders(Product $product)    {        $orders = $this->httpClient->get(sprintf('/product/%d/orders', $product->getId()));        $orders = $this->hydrateResponseToOrdersInSomeWay($orders);        return $orders;    }}

You can even make some methods use the http client and some use the database in a single repository.

Register your repositories as services and use them rather then calling Doctrine::getRepository() directly:

services:    repository.orders:        class: DoctrineOrders        arguments:            - @doctrine.orm.entity_manager

Always rely on your repository interfaces and never on a specific implementation. In other words, always use a repository interface type hint:

class DefaultController{    private $orders;    public function __construct(Orders $orders)    {        $this->orders = $orders;    }    public function indexAction(Product $product)    {        $orders = $this->orders->findProductOrders($product);        // ...    }}

If you don't register controllers as services:

class DefaultController extends Controller{    public function indexAction(Product $product)    {        $orders = $this->get('repository.orders')->findProductOrders($product);        // ...    }}

A huge advantage of this approach is that you can always change the implementation details later on. Mysql is not good enough for search anymore? Let's use elastic search, it's only a single repository!

If you need to call $product->getOrders() and fetch orders from the API behind the scenes it should still be possible with some help of doctrine's lazy loading and event listeners.