C#•3y ago

✅ Scoped, Singleton and HostedService

Any .NET Masters here? xD

Issue:
I'm trying to create a new Background Service for automatic selling/buying crypto (It's a school project, so no real trading/money involved).
I'm having issues with the activation of the repo/services etc.

I'm adding the Repo to my Service, which has EF Core (Repo).
It has Scoped on the Repository classes.

When I try to add the Service as a Singleton and my background service as a HostedService, I just get an error that It can not activate.

I'm using ASP.NET Core Web API

Any work arounds?

I've tried posting in the DotNetEvolution, but didn't get any response.

TeBeCo•5/21/23, 9:59 AM

I've tried posting in the DotNetEvolution, but didn't get any response.

because that discord is more oriented for contributor / contribution etc ... rather than getting help

TeBeCo•5/21/23, 10:00 AM

your question is too focused on "fixing your issue" rather than understand the issue you're having

TeBeCo•5/21/23, 10:00 AM

I'm not sure that's the case but if I put it bluntly

TeBeCo•5/21/23, 10:00 AM

you might be strugglying (or not) with how DI works

TeBeCo•5/21/23, 10:01 AM

let's try to help here

TeBeCo•5/21/23, 10:01 AM

I'll start with basics so we're on the same line

TeBeCo•5/21/23, 10:01 AM

what does transient means do you ?

TeBeCo•5/21/23, 10:01 AM

(i'll ask obvious question first)

TeBeCo•5/21/23, 10:01 AM

just to clarify basic DI things

TeBeCo•5/21/23, 10:01 AM

and we'll move to your actual issue

TTeBeCo > I've tried posting in the DotNetEvolution, but didn't get any response. becaus...

julianOP•5/21/23, 10:02 AM

I've been looking at the different DI.
Transient - It's created everytime it's requested, If I'm not wrong

TeBeCo•5/21/23, 10:02 AM

yeah

TeBeCo•5/21/23, 10:02 AM

ok singleton now

julianOP•5/21/23, 10:03 AM

One instanse created?

TeBeCo•5/21/23, 10:03 AM

yep

TeBeCo•5/21/23, 10:03 AM

now the funky one ...

TeBeCo•5/21/23, 10:03 AM

Scoped

TeBeCo•5/21/23, 10:04 AM

spoiler: the answer is in the name

julianOP•5/21/23, 10:05 AM

Within it's scope?

TeBeCo•5/21/23, 10:05 AM

yeah

TeBeCo•5/21/23, 10:05 AM

a scoped injection create an instance ONLY ONE per scope

TeBeCo•5/21/23, 10:05 AM

that's the trick

TeBeCo•5/21/23, 10:05 AM

now ... the actual question is ... when are Scope created

TeBeCo•5/21/23, 10:05 AM

so let's start with a very bad assumption here

TeBeCo•5/21/23, 10:06 AM

let's forget BackgroundService for a moment

TeBeCo•5/21/23, 10:06 AM

you familliar with Middleware ?

julianOP•5/21/23, 10:06 AM

Yup

TeBeCo•5/21/23, 10:06 AM

this looks familiar I assume ?

julianOP•5/21/23, 10:06 AM

Yup

TeBeCo•5/21/23, 10:06 AM

what is I tell you that low level inside aspnetcore there's one that it role it to craete a scope ?

TeBeCo•5/21/23, 10:07 AM

this means that every thing downstream will transitively respect Scoped registration

TeBeCo•5/21/23, 10:08 AM

so for your DbContext ... that's why your Controller / Services / etc ... respect that

TeBeCo•5/21/23, 10:08 AM

because GENERALLY your controller / Service SHOULD BY DEFAULT always be though as

TeBeCo•5/21/23, 10:08 AM

is that still ok for now ?

julianOP•5/21/23, 10:09 AM

Yupp, still ok

TeBeCo•5/21/23, 10:09 AM

ok so where in the code do you generally indicate that you want injection to happen ?

julianOP•5/21/23, 10:09 AM

In the constructor?

TeBeCo•5/21/23, 10:09 AM

yep

TeBeCo•5/21/23, 10:10 AM

so if your Service is Transient ... as per above, how often is called the ctor ? and thus how often the injection ?

TeBeCo•5/21/23, 10:10 AM

(we're almost there ^^)

julianOP•5/21/23, 10:10 AM

Everytime the class is called?

TeBeCo•5/21/23, 10:11 AM

everytime that class is also injected

TeBeCo•5/21/23, 10:11 AM

(wording is important here)

TeBeCo•5/21/23, 10:11 AM

ok now ...

TeBeCo•5/21/23, 10:11 AM

Singleton

TeBeCo•5/21/23, 10:11 AM

how many time the ctor of a singleton is called ?

julianOP•5/21/23, 10:12 AM

Once during the lifetime of the application

TeBeCo•5/21/23, 10:12 AM

yes and no