monolog.logger.db service has been removed - symfony

Question

I'm trying to refactor some Symfony 3 code to Symfony 4.
I am getting the following error when attempting to log:
The "monolog.logger.db" service or alias has been removed or inlined
when the container was compiled. You should either make it public, or
stop using the conta iner directly and use dependency injection
instead.
My logging code:
$logger = $container->get('monolog.logger.db');
$logger->info('Import command triggered');
Monolog config:
monolog:
channels: ['db']
handlers:
db:
channels: ['db']
type: service
id: app.monolog.db_handler
app.monolog.db_handler config (Note, I tried public: true here and it had no affect:
app.monolog.db_handler:
class: App\Util\MonologDBHandler
arguments: ['#doctrine.orm.entity_manager']
How can I get this wired up correctly in Symfony 4?

Answer 1

By default all services in Symfony 4 are private (and is the recommended pratice) so you need to "inject" in each Controller each needed service (personally I use a custom CommonControllerServiceClass).
You can also create a public service "alias" to continue accessing the service as you did, but it's not the best pratice to follow (also because I guess you will have many other services to fix).
mylogger.db:
alias: monolog.logger.db
public: true
then you can get the service from the container:
$logger = $container->get('mylogger.db');

Answer 2

Alister's answer is a good start, but you can utilise service arguments binding instead of creating a new service for each logger:
services:
_defaults:
autowire: true
bind:
$databaseLogger: '#monolog.logger.db'
Then just change the argument name in your class:
// in App\Util\MonologDBHandler.php
use Psr\Log\LoggerInterface;
public function __construct(LoggerInterface $databaseLogger = null) {...}

Answer 3

It appears that App\Util\MonologDBHandler may be the only thing that is actively using monolog.logger.db - via a container->get('...') call. (If not, you will want to use this technique to tag the specific sort of logger into more services).
You would be better to allow the framework to build the app.monolog.db_handler service itself, and use the container to help to build it. Normally, to inject a logger service, you will just need to type-hint it:
// in App\Util\MonologDBHandler.php
use Psr\Log\LoggerInterface;
public function __construct(LoggerInterface $logger = null) {...}
However, that will, by default, setup with the default #logger, so you need to add an extra hint in the service definition of the handler that you want a different type of logger:
services:
App\Log\CustomLogger:
arguments: ['#logger']
tags:
- { name: monolog.logger, channel: db }
Now, the logger in CustomLogger should be what you had previously known as monolog.logger.db.
You can also alias a different interface (similar to how the LoggerInterface is aliased to inject '#logger') to the allow for the tagging.