Castle.Windsor, ASP.NET MVC, Handling Null Resolution of Injection

Using Castle.Windsor in ASP.NET MVC (3.0) is there any way I can appropriately handle if one of my dependencies resolves null? For instance, say I have a IMembershipService.

class ServiceInstaller
{
 // ... 
 void Install( // .. )
 { 
  container.Register(
  Component
  .For<IMembershipService>()
  .ImplementedBy<MembershipService>()
  .LifeStyle.PerWebRequest
  );
 }
}

Okay, this works great. Now, perhaps not all of my si开发者_运维知识库te requires a user to be logged in. Let's assume that maybe my web host's database server crashes for a few hours. In that event, things that looked into the database, or tried to call on my ISession might return null.

What can I do in this case? I can write if(membershipService == null) a hundred times over, but that seems pretty dumb. Is there a built-in solution to say "Hey, if we have an error, do this..?"

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I think that the service should never be null. If the database is down, the service should be returned nevertheless, but its methods should throw an exception, return null or some default value, depending on the semantic of the service.

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Ciel, i had this problem just recently and found your question while looking for the answer.

Basically you should be using a typed factory to resolve your components at runtime in your wrapping component. The factory should return a default object if there is no match regarding the component you're looking for, default object that would implement whatever behavior is needed.

In the case of your IMembershipService, implement a NotCheckingMembershipService class inheriting the interface and doing nothing and make it the default for the components that won't need it. More specific membership services can be linked to specific controllers.

To do so you must create a generic "catch-all" implementation

public class NotCheckingMembershipService<T>: IMembershipService<T> where T: Controller
{
}

And register it as the default component for an open IMembershipService

_container.Register(
            Component.For(typeof(IMembershipService<>))
            .ImplementedBy(typeof(NotCheckingMembershipService<>))
            .IsDefault());

Then simply register your custom membership services where needed. Resolution won't fail and you will always be able to call the interface.