How to use monolog from the class which inherit Controller class - symfony

Question

I am using monolog
in class DefaultController extends Controller
such as
$logger = $this->get('logger');
$logger->info('Get Started');
I can call this->get('logger') from the class which inherits Controller class.
However I want to use logger from other class such as /Entity/User.php
How can I make it?
my reference is
http://symfony.com/doc/2.0/cookbook/logging/monolog.html

Answer 1

In general you can access services like the logger in classes where the container is not automatically injected ( i.e. Controller and Commands extending ContainerAwareCommand ) by using Dependency Injection.
Possible injection-types are property-,setter- and constructor injection. My example will cover constructor injection. you will first need to create a service for your class.
Assuming yml-configuration an example could look like this:
services:
your_service:
class: Vendor/YourBundle/NonControllerExtendingClass
arguments: ["#logger"] # inject logger service into constructor
In my example the 'logger' service is automatically injected in the NonControllerExtendingClass if it is called as a service. Make sure you have something like this in your Vendor/YourBundle/NonControllerExtendingClass:
use Symfony\Component\HttpKernel\Log\LoggerInterface;
// ...
public function __construct(LoggerInterface $logger)
{
$this->logger = $logger;
}
now use the logger in your method like this:
public function someAction()
{
$this->logger->info('Im here');
}
The logger will only be injected if you call your class as a Service or inject the logger manually.
// ... gets service from the container
$my_service = $this-container->get('your_service');
// ... manual injection
$logger = $this->container->get('logger');
// alternatively create a logger object yourself i.e. $logger = new Logger();
$my_service = new Vendor/YourBundle/NonControllerExtendingClass($logger);
If you want to track entity changes with the logger you should use a Doctrine Event Listener or Subscriber.
Readmore about it in the documentation chapter - How to Register Event Listeners and Subscribers.

Answer 2

Because of separation of concerns, entities should not have dependencies on services. Depending on your needs, it might be wise to use the logger from the controller/service or whatever that calls the entities method that you want to log.
Generally speaking, you can define classes as services and inject the logger into that service. If you are not yet familiar with the service container and dependency injection, I would strongly advise you to read this chapter of the docs.
It might be a tricky subject to grasp. However, as it is such a vital component of symfony, it will be really worth your while to try to understand this.