Application-wide repository

Question

I'm working on a new webproject and I've encountered a problem which I never quite seems to figure out how to do correctly. My application is to use a repository that should be accessible from the entire application. Specifically it needs to be callable from ASP.NET MVC ActionFilters.

Any thoughts on the subject?

Answer 1

It looks like you are either looking for the singleton pattern or an Dependency Injection container (like Castle Windsor or Unity) configured with a singleton lifetime for the object.

In a singleton, you put a static "Instance" property accessor on the object and have it always return the same instance. Two things to note on the singleton pattern though:

1. There are threading issues, which are covered by the MSDN doc on singletons
2. It is generally considered an anti-pattern as it promoted class coupling

Using a DI container, objects are constructed automatically with any dependencies (constructor arguments). Objects configured with a "singleton lifetime" will only every be constructed once and the instance shared with all objects that depend on it (beware threading issues).

// The repository argument will be resolved by the DI container
public ObjectConstructor(IRepositoryInterface repository)
{
    this.repository = repository;
}

In the case of Attributes (like ActionFilters), where the class is constructed by the runtime, you would access the container (or an abstraction of it) directly and request your instance:

this.repository = Container.Instance.Resolve<IRepositoryInterface>();