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Dependency Injection

Drush command files obtain references to the resources they need through a technique called dependency injection. When using this programing paradigm, a class by convention will never use the new operator to instantiate dependencies. Instead, it will store the other objects it needs in class variables, and provide a way for other code to assign an object to that variable.

Tip

Drush 11 and prior required dependency injection via a drush.services.yml file. This approach is deprecated in Drush 12+.

Autowire

12.5+

Command files may inject Drush and Drupal services by adding the AutowireTrait to the class (example: PmCommands). This enables your Constructor parameter type hints to determine the injected service. When a type hint is insufficient, an #[Autowire] Attribute on the constructor property (with service: named argument) directs AutoWireTrait to the right service (example: FieldDefinitionCommands). Some autowire examples:

protected readonly Consolidation\OutputFormatters\FormatterManager $formatterManager
protected readonly Psr\Log\LoggerInterface $logger
protected readonly Drush\SiteAlias\ProcessManager $processManager
protected readonly Consolidation\SiteAlias\SiteAliasManagerInterface $siteAliasManager
protected readonly \Drush\Config\DrushConfig $drushConfig
protected readonly Drupal\Core\Entity\EntityTypeManagerInterface $entityTypeManager

If your command is not found by Drush, add the -vvv option for debug info about any service instantiation errors. If Autowire is still insufficient, a commandfile may implement its own create() method (see below).

create() method

11.6+

Command files not using Autowire may inject services by adding a create() method to the commandfile. The passed in Container is a League container with a delegate to the Drupal container. Note that the type hint should be to Psr\Container\ContainerInterface not Symfony\Component\DependencyInjection\ContainerInterface. A create() method and constructor will look something like this: 

class WootStaticFactoryCommand extends Command
{
    protected $configFactory;

    protected function __construct($configFactory)
    {
        $this->configFactory = $configFactory;
    }

    public static function create(Psr\Container\ContainerInterface $container): self
    {
        return new static($container->get('config.factory'));
    }
See the Drupal Documentation for details on how to inject Drupal services into your command file. This approach mimics Drupal's blocks, forms, and controllers.

Inflection (deprecated)

Command classes used to implement the following interfaces. The replacement approach is listed below.