Injecting parameter based service into other service - symfony

Question

I have a service which takes a driver to do the actual work. The driver itself is within the context of Symfony 2 is just another service.
To illustrate a simplified version:
services:
# The driver services.
my_scope.mailer_driver_smtp:
class: \My\Scope\Service\Driver\SmtpDriver
my_scope.mailer_driver_mock:
class: \My\Scope\Service\Driver\MockDriver
# The actual service.
my_scope.mailer:
class: \My\Scope\Service\Mailer
calls:
- [setDriver, [#my_scope.mailer_driver_smtp]]
As the above illustrates, I can inject any of the two driver services into the Mailer service. The problem is of course that the driver service being injected is hard coded. So, I want to parameterize the #my_scope.mailer_driver_smtp.
I do this by adding an entry to my parameters.yml
my_scope_mailer_driver: my_scope.mailer_driver_smtp
I can then use this in my config.yml and assign the parameter to the semantic exposed configuration [1]:
my_scope:
mailer:
driver: %my_scope_mailer_driver%
In the end, in the Configuration class of my bundle I set a parameter onto the container:
$container->setParameter('my_scope.mailer.driver', $config['mailer']['driver'] );
The value for the container parameter my_scope.mailer.driver now equals the my_scope.mailer_driver_smtp that I set in the parameters.yml, which is, as my understanding of it is correct, just a string.
If I now use the parameter name from the container I get an error complaining that there is no such service. E.g:
services:
my_scope.mailer:
class: \My\Scope\Service\Mailer
calls:
- [setDriver, [#my_scope.mailer.driver]]
The above will result in an error:
[Symfony\Component\DependencyInjection\Exception\ServiceNotFoundException]
The service "my_scope.mailer" has a dependency on a non-existent service "my_scope.mailer.driver"
The question now is, what is the correct syntax to inject this container parameter based service?
[1] http://symfony.com/doc/current/cookbook/bundles/extension.html

Answer 1

This question has a similar answer here
I think the best way to use this kind of definition is to use service aliasing.
This may look like this
Acme\FooBundle\DependencyInjection\AcmeFooExtension
public function load(array $configs, ContainerBuilder $container)
{
$configuration = new Configuration;
$config = $this->processConfiguration($configuration, $configs);
$loader = new Loader\YamlFileLoader(
$container,
new FileLocator(__DIR__.'/../Resources/config')
);
$loader->load('services.yml');
$alias = $config['mailer']['driver'];
$container->setAlias('my_scope.mailer_driver', $alias);
}
This will alias the service you've defined in my_scope.mailer.driver with my_scope.mailer_driver, which you can use as any other service
services.yml
services:
my_scope.mailer_driver:
alias: my_scope.mailer_driver_smtp # Fallback
my_scope.mailer_driver_smtp:
class: My\Scope\Driver\Smtp
my_scope.mailer_driver_mock:
class: My\Scope\Driver\Mock
my_scope.mailer:
class: My\Scope\Mailer
arguments:
- #my_scope.mailer_driver
With such a design, the service will change whenever you change the my_scope.mailer_driver parameter in your config.yml.
Note that the extension will throw an exception if the service doesn't exist.

Answer 2

With service container expression language you have access to the following two functions in config files:
service - returns a given service (see the example below);
parameter - returns a specific parameter value (syntax is just like service)
So to convert parameter name into a service reference you need something like this:
parameters:
my_scope_mailer_driver: my_scope.mailer_driver_smtp
services:
my_scope.mailer:
class: \My\Scope\Service\Mailer
calls:
- [setDriver, [#=service(parameter('my_scope_mailer_driver'))]]

Answer 3

At first I thought this was just a question of getting the # symbol passed in properly. But I tried assorted combinations and came to the conclusion that you can't pass an actual service as a parameter. Maybe someone else will chime in and show how to do this.
So then I figured is was just a question of using the service definition and passing it a reference. At first I tried this in the usual extension but the container does not yet contain all the service definitions.
So I used a compiler pass: http://symfony.com/doc/current/cookbook/service_container/compiler_passes.html
The Pass class looks like:
namespace Cerad\Bundle\AppCeradBundle\DependencyInjection\Compiler;
use Symfony\Component\DependencyInjection\Compiler\CompilerPassInterface;
use Symfony\Component\DependencyInjection\ContainerBuilder;
use Symfony\Component\DependencyInjection\Reference;
class Pass1 implements CompilerPassInterface
{
public function process(ContainerBuilder $container)
{
// Set in the Extension: my_scope.mailer_driver_smtp
$mailerDriverId = $container->getParameter('my_scope.mailer.driver');
$def = $container->getDefinition('my_scope.mailer');
$def->addMethodCall('setDriver', array(new Reference($mailerDriverId)));
}
}
Take the calls section out of the service file and it should work. I suspect there is an easier way but maybe not.

Answer 4

#my_scope.mailer.driver needs to be a service but not defined as service. To retrieve string parameter named as my_scope.mailer.driver you need to wrap it with %: %my_scope.mailer.driver%.
So you need to pass #%my_scope.mailer.driver% as parameter to a service. Yml parser will replace %my_scope.mailer.driver% with the appropriate value of the parameter and only then it will be called as a service.