Registering a shared service with a custom factory

Question

I'm wondering how (if I can) register a shared service with a custom factory.

Consider the following code:

class MyApiFactory {
    private $config;

    public function ___construct(Config $config) {
        $this->config = $config;
    }

    //this method could either be __invoke
    //or the class could implement some factory interface
    public function create() {
        return new MyApi($this->config->get('some-value'), $this->config->get('some-other-value'));
    }

}

class MyApi {
}

class MyService1 {
    public function __construct(MyApi $api) {}
}

class MyService2 {
    public function __construct(MyApi $api) {}
}

With other PHP DI frameworks - I would register MyApiFactory as a factory for MyApi. If I requested for service MyService1 the DI container would see that It needs MyApi and therefore execute MyApiFactory to get MyApi - MyApi would then be stored as a service (if the container supports sharing).

Then I ask for MyService2 which also needs MyApi - as MyApi has already been created before - it just pulls it from the DI container and injects it in MyService2.

Therefore MyApi in MyService1 & MyService2 are the same.

I can't seem to find a way to do this in Magento 2. Basically I want to avoid creating MyApi twice.

The only way I can think to do this is to keep a record of the created MyApi inside MyApiFactory so the second time MyApiFactory::create is called it returns the existing instance. Then I would have to inject MyApiFactory into MyService1 & MyService2 and call create within there constructors or wherever.

This (to me) seems wholly unnecessary and quite unintuitive - is this a problem anyone else has come across? Is there some support for shared services with custom factories in Magento 2 ?

This was more of a question to the Magento 2 developers rather than the community, I did originally create this as an issue but that got shut down, refs: https://github.com/magento/magento2/issues/8182#issuecomment-273763661

Answer 1

It seems like you misunderstood the DI logic for Magento 2...

Factory usage

interface MyApiInterface {
}

class MyApi implements MyApiInterface {
}

class MyService1 {
    public function __construct(MyApiInterfaceFactory $apiFactory) {
        /** @var MyApiInterface $api */
        $api = $apiFactory->create();
    }
}

class MyService2 {
    public function __construct(MyApiInterfaceFactory $apiFactory) {
        /** @var MyApiInterface $api */
        $api = $apiFactory->create();
    }
}

Factories will be autogenerated by Magento Framework...

Singletons

In your case you want instanciate MyApi as a singleton in order to use the same instance in all services. In this case the code should look like following:

interface MyApiInterface {
}

class MyApi implements MyApiInterface {
}

class MyService1 {
    public function __construct(MyApiInterface $api) {}
}

class MyService2 {
    public function __construct(MyApiInterface $api) {}
}

Just use your MyApiInterface as type hint in the constructor and Magento will inject the same instance of MyApi each time...

Of course you need to define the preference for your MyApiInterface in di.xml...

Own factory

interface MyApiInterface {
}

interface MyApiFactoryInterface {
    public function create(...): MyApiInterface
}

class MyApiFactory implements MyApiFactoryInterface {
}

class MyApi implements MyApiInterface {
}

class MyService1 {
    public function __construct(MyApiFactoryInterface $apiFactory) {
        $api = $apiFactory->create();
    }
}

class MyService2 {
    public function __construct(MyApiFactoryInterface $apiFactory) {
        $api = $apiFactory->create();
    }
}

In this case Magento will inject each time the same instance of your factory. So the factory become kind of a singleton...