114. How many Instances of Service Should It Be

Jul 15, 2026 04:41 · 2:12 · English · Whisper Turbo · 2 Reproduktory
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S… Speaker 2 (114. How many Instances of Service Should It Be)
In the last lecture,
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S… Speaker 2 (114. How many Instances of Service Should It Be)
we learned about that hierarchical injector.
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And actually,
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this injection behavior leads to the behavior we see here.
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Now,
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that's not a bug that's intended.
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You might have an application where you want to have many different
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instances of the same service,
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where you absolutely don't want to have the same instance.
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But sometimes you want to have the same instance.
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And we definitely do.
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Because right now for our account service,
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we have three instances.
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S… Speaker 2 (114. How many Instances of Service Should It Be)
The first one gets created here in AppComponent.
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S… Speaker 2 (114. How many Instances of Service Should It Be)
We provide it here.
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AppComponent receives its own service or its own instance of the service,
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S… Speaker 2 (114. How many Instances of Service Should It Be)
I should say, as do all the child components.
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S… Speaker 2 (114. How many Instances of Service Should It Be)
Now you might say,
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fine, because new account and account are child components,
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right?
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But there we provide it again,
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S… Speaker 2 (114. How many Instances of Service Should It Be)
and hence we override the instance we would get from the app component.
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Now new account and account component have
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their own instances.
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S… Speaker 2 (114. How many Instances of Service Should It Be)
So these are the other two instances of this service class.
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S… Speaker 2 (114. How many Instances of Service Should It Be)
And therefore,
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S… Speaker 2 (114. How many Instances of Service Should It Be)
if we add a new service,
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we call add account,
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S… Speaker 2 (114. How many Instances of Service Should It Be)
there we push it on this array of accounts,
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and this actually works,
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but it's a totally different instance of the service than the one
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S… Speaker 2 (114. How many Instances of Service Should It Be)
we use here in app component,
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the one through which we loop.
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How can we fix it then here for our app?
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Simple.
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We just remove it from the provider's array.
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S… Speaker 2 (114. How many Instances of Service Should It Be)
Don't remove it from the constructor.
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S… Speaker 2 (114. How many Instances of Service Should It Be)
We of course do need it here,
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S… Speaker 2 (114. How many Instances of Service Should It Be)
because that tells Angular that we want an instance.
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S… Speaker 2 (114. How many Instances of Service Should It Be)
The provider's array basically tells which instance,
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so there we needed to remove it.
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S… Speaker 2 (114. How many Instances of Service Should It Be)
And the same for account component.
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S… Speaker 2 (114. How many Instances of Service Should It Be)
Leave it in the constructor,
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S… Speaker 2 (114. How many Instances of Service Should It Be)
leave the import at the top,
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S… Speaker 2 (114. How many Instances of Service Should It Be)
but remove it from the provider's array.
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S… Speaker 2 (114. How many Instances of Service Should It Be)
With that little change,
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S… Speaker 2 (114. How many Instances of Service Should It Be)
if we go back to the application after saving it,
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S… Speaker 2 (114. How many Instances of Service Should It Be)
let's add another account.
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S… Speaker 2 (114. How many Instances of Service Should It Be)
Now you see it at the bottom.
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S… Speaker 2 (114. How many Instances of Service Should It Be)
Now you can change the status again.
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S… Speaker 2 (114. How many Instances of Service Should It Be)
So this is the difference.
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S… Speaker 2 (114. How many Instances of Service Should It Be)
Different instances of the service.
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S… Speaker 2 (114. How many Instances of Service Should It Be)
Now we're using one and the same before we weren't.
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S… Speaker 2 (114. How many Instances of Service Should It Be)
Both may be the behavior you want in your app,
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S… Speaker 2 (114. How many Instances of Service Should It Be)
but make sure that you get the correct one.

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