Dependency injection in domain object extension methods

I'm creating a node based web CMS system in asp.net mvc.

Having read some books on dependency injection I've split my solution up into multiple projects and using abstractions (abstract classes and interfaces).

I can't figure out how to solve the following type of code in my web project:

myDomainObjectNode.GetChildNodes<SomeSubNodeClass>();

I could accomplish this if the domain object had a reference to an INodeRepository but that would mean that I have to carry this dependency around in all domain objects which is a hassle, especially when having to create new instances. Is having dependencies (mainly repositories) in you domain object a bad thing?

My other idea is to achieve this using extension methods. However, extension methods are static on a static class which itself cannot be cons开发者_开发问答tructed using an IoC. I could solve this using a Singleton for the INodeRepository and having it set by the IoC.

This doesn't feel like an elegant solution... do you have any other ideas or input?

Thank you!

I typically avoid giving a domain object access to repositories and hide any persistence concerns as much as possible.

When you create your myDomainObjectNode you could also fill a collection of childnodes to hold concrete object references. This would typically be a concern for a builder or factory.

I'd probably drop the generic type to filter the collection and just use Linq, your childnodes collection could return a IEnumerable<BaseNode>.

Of course you can augment it with various deferred loading and caching strategies, something a typical ORM can help you with.

If you do decide to use a repository from your domain object I would favor to inject it through the constructor. This makes the dependency explicit and you externalize it's scope.

I ended up solving this using the MVC DependencyResolver to get an INodeService inside an extension-method in the MVC web project. Works like a charm and I don't think I've broken any serious OO-patterns.