Question

In an application I have the following components (among others):

• MyDbContext : Entity framework data access
• DBResourceProviderFactory : A custom ResourceProviderFactory providing a custom IResourceProvider (called DBResourceProvider…)
• Other services
• StructureMap

The custom resource provider is looking resources up in the db using MyDbContext, injected similarly as described in this SO answer.

The MyDbContext is also used in various other services, and since it is a web application, I use StructureMaps HttpContextScoped method to limit the lifetime of MyDbContext to the lifetime of the request (see an other SO question and its answer on this subject):

x.For<MyDbContext>().HttpContextScoped();

However, it seems that the lifetime of an IResourceProvider is not limited to a single http request. Therefore, DBResourceProvider keeps hanging onto a MyDbContext reference which will be disposed after the first request.

How can I handle this lifetime mismatch – have StructureMap return a transient MyDbContext for IDbResourceProvider while returning HttpContext-scoped instances to all other services?

Do I need two different implementations to do that? A marker interface?
Or is it a bad idea to use Entity Framework to look up localized resources in the first place (performance etc.)?

Answer 1

If you have a service that has (or needs to have) a long lifetime than (one of) its dependencies, the general solution is to use a factory to get those dependencies.

In your situation the solution might be simple. When your DBResourceProvider is defined in your composition root of your MVC application, it would simply succeed to use the DependencyResolver.Current.GetService method to get the MyDbContext.

When the DBResourceProvider service isn’t part of the composition root (for instance because it contains business logic that you need to test), you could either extract that logic into its own class, to allow the service to be in the composition root, or you can inject a (singleton) factory (for instance IDbContextFactory or Func<MyDbContext>) that allows you to get the proper instance to be resolved.