Inject EntityManager in a service from another service - php

Question

I'm extracting code from Controller to a kind of ApplicationService in a Symfony 3.4 App.
I've a concrete class for scraping data and another concrete transformer to change some data.
src\App\Service
class CompanyScraping implements ScrapingInterface
{
private $crawler;
public function __construct(CrawlerInterface $crawler)
{
$this->crawler = $crawler;
}
public function extract()
{
...
}
public function transform()
{
$transformer = new concreteTransformer();
}
}
class concreteTransformer
{
private $em;
public __construct(EntityManagerInterface $em)
{
$this->em = $em;
}
}
How could I pass the EntityManager to the concreteTransformer class if the EntityManager is not called in CompanyScraping class? I can't instantiating concreteTransformer with a new.
I'm thinking in this two options:
Pass EntityManager to CompanyScraping, but I thik that is a wrong idea because CompanyScraping doesn't need this dependency.
Extract transform method into a another class and pass the em from controller/console
$crawler = new CompanyScraping(new GoutteClient());
$rawData = $crawler->extract(...);
$data = new concreteTransformer($em, $rawData);
Any other idea?
Thanks.

Answer 1

The first solution I thought of is to inject (not the EM, but) the Transformer into the Scraper class, as posted in the comments.
Such solution would, however, not address the underlying problem: is the Scraper scraping, transforming or both? In the latter case, it's not adhering to the single responsibility principle, because it has the responsibility for both scraping and transforming.
A design pattern that could be pretty effective to tackle this, is the decorator pattern.
The idea in this case is to "decorate" the scraped results with a transformation.
The result would look somewhat like this:
class Transformer implements ScrapingInterface
{
private $scraper;
private $em;
public __construct(ScrapingInterface $scraper, EntityManagerInterface $em)
{
$this->scraper = $scraper;
$this->em = $em;
}
public function extract()
{
return $this->transform($this->scraper->extract());
}
private function transform() {...}
}
It can be constructed as:
$crawler = new Transformer(new CompanyScraping(new GoutteClient()), $em);
In case you have multiple transformer implementations, you can make the decorator more generic:
class TransformingScraper implements Scraper
{
private $scraper;
private $transformer;
public __construct(Scraper $scraper, Transformer $transformer)
{
$this->scraper = $scraper;
$this->transformer = $transformer;
}
public function extract()
{
return $this->transformer->transform($this->scraper->extract());
}
}
$crawler = new TransformingScraper(
new CompanyScraping(new GoutteClient()),
new ConcreteTransformer($em)
);