Microsoft DI GetService consistency

[stephenlautier]

Since we switched to Grace, several Microsoft DI extensions seems a bit inconsistent when using GetService and GetRequiredService.

• Given AllowInstanceAndFactoryToReturnNull = true

  • when service is not registered
    • and GetRequiredService is invoked should throw - currently its not throwing
    • and GetService is invoked should NOT throw - working fine

• Given AllowInstanceAndFactoryToReturnNull = false

  • when service is not registered
    • and GetRequiredService is invoked should throw - working fine
    • and GetService is invoked should NOT throw - currently its throwing

Basically GetService and GetRequiredService should work as the name suggests - GetRequiredService should always throw; GetService shouldnt throw.

What do you think?

[ipjohnson]

@stephenlautier can you create a simple example showing your use case. The reality is you are mixing to different ideas together in one case you are telling the container you specifically don't want it to throw an exception if you return null yet you want it to throw an exception when you return null.

[ipjohnson]

@stephenlautier In regards to your proposal:

• AllowInstanceAndFactoryToReturnNull = true GetRequiredService not throwing an exception is an incorrect behavior and I think should be addressed.

• AllowInstanceAndFactoryToReturnNull = false I look at differently. Grace doesn't hide errors in it's "Try" methods. If an exception or a dependency is missing in an object graph an exception is thrown even in a "Try". Registering a Factory and then returning null is considered an error in Grace (you're agreeing to provide a dependency then choosing not to).

I'll look into changing the behavior for AllowInstanceAndFactoryToReturnNull = true

[stephenlautier]

Yes, to be honest I wasn't 100% sure with the AllowInstanceAndFactoryToReturnNull = false and GetService whether it should throw or not. The reason i concluded that maybe it should be like that because if you would use a library which might use GetService internally and its optional, you will get different behaviors. Infect i had this issue, since we had one optional service in a specific case, so had to enable AllowInstanceAndFactoryToReturnNull.

So basically what i was then more in favor is to be as following

• GetService = optional
• GetRequiredService = mandatory
• Any other constructor injections without using GetService directly will be controlled via the config (not sure if it make sense tho since most probably it will call GetService itself internally

Just a suggestion ofc, but the main one was the GetRequiredService. Thanks!

[ipjohnson]

@stephenlautier for the moment I'm going to just address the GetRequiredService problem but at some point I'll probably add an AllowNull method for exporting factories and turn it on for factories coming from the service collection for compatibility sake.

I've pushed a beta to nuget with a null reference check for GetRequiredService let me know how it works

[stephenlautier]

@ipjohnson thats good enough for me, thanks!

[ipjohnson]

@stephenlautier did this take care of it for you?

[stephenlautier]

@ipjohnson yes it seems fine now. sorry for the late response