Angular 2 dependency injection: Inject multiple instances

Question

I have a "Messages" injectable that represents a service that can fetch a user's messages. This class depends on a "Database" class that logs in to the backend using the credentials of the user.

Now I want to write a test case during which 2 users are logged in at the same time, in order to test automatically whether messages sent from user 1 arrive directly at the inbox of user 2.

Therefore, I need a way to inject two different instances of "Messages" with two different, corresponding instances of "Database".

I tried the following:

  beforeEachProviders(() => [
    Messages, Database
  ]);

  beforeEach(inject([Messages], (msg) => {
    this.msg1 = msg;
  }));

  beforeEach(inject([Messages], (msg) => {
    this.msg2 = msg;
  }));

However, it turns out that msg1 and msg2 represent the same instance of "Messages":

it('testcase', () => {
  // this.msg1 == this.msg2;
});

Is it possible to tell the injector to create different instances of "Messages" and its dependencies?

Günter Zöchbauer · Accepted Answer · 2016-06-21 13:02:59Z

1

This is how Angular DI works. For a single provider you always get the same instance.

As a workaround you could inject Injector and use

var child = ReflectiveInjector.fromResolvedProviders(
  ResolvedReflectiveProvider([Message, Database]), injector);
var msg2 = child.get(Message);

This way you should get a different instance of Message and Database while other providers are reused from the parent injector (like MockBackend, ...)`

You can also use

var injector = ReflectiveInjector.resolveAndCreate([Message, Database]);
var msg2 = child.get(Message);

But this way you need to provide all dependencies, not only Message and Database because there is no parent.

edited Jun 21, 2016 at 13:02

answered Jun 21, 2016 at 12:31

Günter Zöchbauer

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3 Comments

highwaychile Over a year ago

Thank you for your answer, but I get this error: pastebin.com/raw/56N7sfZ9 I used this code: pastebin.com/raw/5kh2ZHvD

highwaychile Over a year ago

sorry, hit enter too early: I get this error: pastebin.com/raw/56N7sfZ9 I used this code: pastebin.com/raw/5kh2ZHvD

Günter Zöchbauer Over a year ago

I got it wrong how to create child injectors. I updated my answer.

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