How to elegantly log inside a Doctrine2 entity - symfony

Question

Consider the following situation. I have an entity that holds some information, let's say a news item. This news item contains comments.
In the news item entity, there is calculateStatistics() function, that returns some statistics derived from the news item entity, plus its comments. I used to have this calculate function inside a NewsService, but then found out a service wasn't needed because I only use information that is inside the entity.
Nowadays, the calculate function also does some sanity checking. I want to log negative results as a warning in my Monolog service. I still believe at this point it is valid to have this calculate function inside the entity, since no external information/service is needed. Is there an elegant way to support logging inside an entity?

Answer 1

I don't think that handling logging inside Entity is a good idea, as entity should be as independent as possible and have no business logic inside. I would suggest doing it by event listener. Consider such configuration (I assume you're using Doctrine and want to perform logging while some doctrine event - but if not, you will only have to modify name of event which you listen to):
Entity:
class YourEntity implements StatisticInterface
{
(...)
public function calculateStatistics()
{
(...)
}
}
config.yml
your_service.statistics_listener:
class: Acme\DemoBundle\EventListener\Entity\StatisticsEntityListener
arguments: [#logger]
tags:
- { name: doctrine.event_listener, event: prePersist }
prePersist is one of many possible events, just pick one that fits most
StatisticsEntityListener
class StatisticsEntityListener
{
public function __construct(Logger $logger)
{
$this->logger = $logger;
}
/**
* #param LifecycleEventArgs $args
*/
public function prePersist(LifecycleEventArgs $args)
{
$entity = $args->getEntity();
if ($entity instanceof StatisticInterface) {
//do whatever you like with your logger and entity
$logger->log($entity->calculateStatistics());
}
}
}
This way you get nice separation of concerns and you're able to log info using your Monolog