Registry / Container reform

[dgeb]

RFC

[mixonic]

For Ember-Data we use DS._setupContainer:

• https://github.com/emberjs/data/blob/87dec3e56b6b1744c49103417cc8cacc8f1edb23/packages/ember-data/lib/setup-container.js#L7

If Ember only needs to register/inject, then I would prefer such a hook since they can be easily layered onto a single registry in an arbitrary order.

However I note that you suggest the name be isolatedApplicationInstance - does this imply you will return a real instance and not simply a container with a configured registry?

[dgeb]

Yes. If Container is private and only accessible through an ApplicationInstance, then I believe that's the level at which it should be available for testing.

[workmanw]

With the recent container / registry split we were burned pretty badly with our test helpers. We had created quite a few helpers to do proper testing setup/mocking/teardown/etc. I personally am a little weary of the idea of isolating these given that interaction with the container had previously been encouraged for testing and other initializers.

I guess I have no real concrete reason as to this shouldn't be done, other than I don't really want to refactor all my test helpers again.

[tomdale]

Big, big 👍. I think this proposal kills several 🐦s with one stone:

1. Simplifies initializers: it was mega confusing knowing whether to call register/inject on the application or the container/registry.
2. Gives us a public API we can support in a forwards-compatible way, while giving us the freedom to continue to tweak the container and registry implementations.

I personally am a little weary of the idea of isolating these given that interaction with the container had previously been encouraged for testing and other initializers.

I can't speak for everyone, of course, but @wycats and I have been very openly against anyone treating the container API as public. There are cases where you have to use it, but there is a reason it is marked private. This proposal allows us to (finally) provide an API we can encourage people to use.

[workmanw]

@tomdale Certainly my primary use case is around testing. Using containers to initialize and mock stuff. But also, it is one of the arguments provided when creating an initializer. And for a period of time, before services people were encourage to used injection this way. This is one of dozens examples that come up when you Google ember dependency injection. http://ember.zone/ember-application-initializers/

Any ways, just to make my position clear, I'm not against it. Just pointing out it might be a source of pain for some folks.

[tomdale]

@workmanw Point taken. With Dan's RFC, assuming you were indeed sticking to initializers and coloring within the lines, the refactor is extremely mechanical: just update all of your initializers and replace container with applicationInstance.

[igorT]

container.has/registry.has have been useful for me in the past, so might be good to expose those as well. They don't seem particularly hard to maintain.

[dgeb]

container.has/registry.has have been useful for me in the past, so might be good to expose those as well. They don't seem particularly hard to maintain.

Seems reasonable. Perhaps has could be exposed as hasRegistration.

[dgeb]

@tomdale Thanks for your support of this proposal.

@workmanw I'm sorry that the churn in this area has already affected you. I initiated much of this churn with the Registry / Container split as part of the SSR refactor. That was a necessary precondition to the Application / ApplicationInstance split that @tomdale and @wycats performed to enable SSR. Only now that their work is nearing completion is it possible to come back to rethink Registry and Container access. I hope the end result of all this work is a clean set of interfaces that shield developers from any complexity introduced by these refactors. And since these interfaces will finally be thoroughly public, we can avoid similar churn and breakage in the future.

[stefanpenner]

most of the in-app usages of container are the result of not having:

1. class level injection rules (not global injection rules, which don't inherit)
2. factory injections are backwards, instances should get references to factories and not the other way around.

beyond that, there exist dynamic situations where has/lookupFactory should be exposed, but lookup should never be exposed as this should have been the result of an injection (lazy or constructor).

[stefanpenner]

Unit don't get initializers. By definition this is then no-longer a unit test. Unit level tests can get collaborates provided as constructor Args, but should have no container awareness. My above comment should help remedy most use-cases where users app code violated this.

[dgeb]

All of Ember's "unit" tests rely on the concept of a container that is initialized. The isolatedContainer is not truly "isolated", but relies on registrations performed by Ember and even Ember Data. I'm sure we can all agree that the code in isolatedContainer is un-DRY and a temporary hack, so let's solve this problem more elegantly.

As the discussion about integration vs. unit testing components makes clear, we need a broader discussion about dependency injection, what's exposed to tests, and ember-cli's conventions regarding integration and unit tests. This goes beyond the scope of this RFC, but definitely overlaps it.

@stefanpenner I'll ping you soon to try to set up that overdue hangout / discussion.

[drogus]

I'm not sure if this is something that fits the scope of this RFC, if that's the case just ignore me.

Lately I've been digging into testing story for Ember.js and one thing bothers me about testing an application with services. At the moment there's no easy way to inject mocked services during acceptance testing, or at least there's no way that I know of. Ember.inject.service looks up factory on a container, which will try to resolve it, so even if a user registers a mock service in the tests setup, it won't be picked up.

It would be great if new public API allowed something like this:

var application = startApp();
var mockService = Ember.Object.extend({
  fetchPosts: function() {
    return [{ title: 'a post' }];
  }
});
application.register('service:storage', mockService);

This would make acceptance tests use a mocked service.

There are multiple ways to handle such behaviour, but all that I know of require preparing code for substitution (like creating adapters in ember-data).

[technomage]

Ideally we will have a way to register a replacement service as described above, using a public API.

In testing comma components this has proven very necessary to isolate issues in the front end vs. the back end code.

[technomage]

That was comms components.

[igorT]

@drogus I am also very interested in the acceptance testing story. I think there are at least three blocking issues:

1. startApp helper in acceptance tests returns an Application and not an ApplicationInstance, so its impossible to overwrite a registration, you can just register in the fallback case.
2. resolver always has precedence over the registered classes emberjs/ember.js#11174
3. this RFC doesn't implement unregister and current unregister doesn't work reliably emberjs/ember.js#11173

[drogus]

@igorT

Yeah, the only workaround I found to overcome this issues is to reopen resolver:

application.registry.resolver.__resolver__.reopen({
  resolve: function(fullName) {
    if(fullName === 'service:storage') {
      return mockService;
    } else {
      return this._super.apply(this, arguments);
    }
  }
});

which is clearly not very elegant and will break with any bigger internal changes.

[dgeb]

Here's one way to solve the acceptance testing story:

• The resolver is set only on the Application, not the ApplicationInstance
• Acceptance tests receive an ApplicationInstance instead of an Application
• Custom registrations can be made on the ApplicationInstance.

In this way, registrations will be resolved in order by:

• The application instance's registry
• The application's resolver
• The application's registry

In this way, mocks can be registered with the application instance and those registrations will take precedent when resolved.

[bf4]

Great, so code such as in ember-islands that finds App.DocPrinterComponent would change as below?

-var container = App.__container__;
-var componentLookup = container.lookup('component-lookup:main');
-var component = componentLookup.lookupFactory('doc-printer',  container);
+var component = App.lookupFactory('doc-printer');

[bf4]

Or would it be like

App.instanceInitializer({

  initialize: function(instance) {
    instance.container.lookupFactory('doc-printer');
  }
});

(h/t al3xnull in slack https://embercommunity.slack.com/archives/needhelp/p1434479693008755 )

[dgeb]

Sorry to miss your earlier question. So the lookup and lookupFactory methods would be exposed directly on the instance, in the same way as register and inject:

App.instanceInitializer({

  initialize: function(instance) {
    instance.lookupFactory('doc-printer');
  }
});

(Note: @stefanpenner has concerns about lookupFactory as it's currently implemented. It may be replaced entirely for 2.0)

[bf4]

alrighty, thanks

[igorT]

@dgeb that means that there is parallel register on the container that delegates to the resolver if there is one but caches locally if there isn't?

[dgeb]

@igorT there is no (non-deprecated) register method on the container. register exists only on registries.

There are two registries now: one on the application instance and one on the application. Each has a register method for custom registrations.

When resolving, the instance's registry "falls back" to the application's registry if it can't resolve. If a resolver is associated with either registry, then it will be consulted before the custom registrations in that registry.

The solution here (which I'm about to PR) is to skip setting the resolver on the instance's registry and only set it on the application's registry. This allows custom registrations made through the instance's registry to take precedence over both the resolver and registrations made on the application's registry.

[igorT]

My bad I misread The resolver is set only on the Application, not the ApplicationInstance as The registry is set only on the Application, not the ApplicationInstance

[dgeb]

Implemented and merged via emberjs/ember.js#11440

Should this RFC just be closed now?

[mixonic]

Yes :-)

The filename should be changed to text/0046-registry-reform.md and the RFC PR and Ember Issue should be added at the top of the text.

[dgeb]

Thanks @mixonic! It's ready for review now.