Extend DI documentation for classes with multiple interfaces

[puschie286]

Is there an existing issue for this?

• I have searched the existing issues

Is your feature request related to a problem? Please describe the problem.

The documentation doesn't describe how exposing the interfaces for a class with multiple interfaces can change the instantiation behavior (for singleton and scoped lifetime)

Describe the solution you'd like

We have 2 behaviors:

1. Single instance for every interface (exposing all interfaces but not the class itself)
2. Shared instance between interfaces (exposing all interfaces and the class itself)

This should be made clear in the ExposeService Attribute section.

But the behavior itself gives you two limits:

1. you cant expose the interfaces only with a shared instance
2. you cant expose the implementation class with separate instances for each interface

( well you can always fall back to manually register those cases )

Additional context

This is somehow surprising: you might try to prevent the usage of the implementation class by only exposing the interfaces but result in having multiple singleton instances (one for each interface).

Maybe this is even classified as bug, because you change the behavior (that is defined by the Dependency attribute) by the way you use the ExposeServices attribute

[maliming]

hi @puschie286

Can you share some code to explain this?

Thanks.

[puschie286]

sure:

interface IFirstSingle;
interface IFirstMulti;
interface ISecondSingle;
interface ISecondMulti;

[ExposeServices( typeof( SingleInstance ), typeof( IFirstSingle ), typeof( ISecondSingle ) )]
class SingleInstance : IFirstSingle, ISecondSingle, ISingletonDependency;

[ExposeServices( typeof( IFirstMulti ), typeof( ISecondMulti ) )]
class MultipleInstances : IFirstMulti, ISecondMulti, ISingletonDependency;

public class TestClass
{
	public void Test( IServiceProvider provider )
	{
		var firstSingle = provider.GetService<IFirstSingle>();
		var secondSingle = provider.GetService<ISecondSingle>();
		
		Debug.Assert( firstSingle == secondSingle );

		var firstMulti = provider.GetService<IFirstMulti>();
		var secondMulti = provider.GetService<ISecondMulti>();
		
		Debug.Assert( firstMulti != secondMulti );
	}
}

its just example code, but this is the behavior you will see when using ABP auto registration process

[maliming]

hi

In this case, you only added 2 services(IFirstMulti and ISecondMulti) to DI. They cannot get a unique implementation because IFirstMulti and ISecondMulti are different.

you can always fall back to manually register those cases

You have to add a new service to the DI to manually register those cases

[ExposeServices( typeof( IFirstMulti ), typeof( ISecondMulti ) )]
class MultipleInstances : IFirstMulti, ISecondMulti, ISingletonDependency;

[puschie286]

Yes, i understand that - but its still somehow surprising that ExposeServices can change the behavior. Would be great if the documentation state something like "If you dont expose the class itself, each interface get their own instance"

[maliming]

Thanks. I will mention this in the document.