DDD repositories as singletons?

Question

Quick question: Would it be a good or a bad idea to implement my domain-driven design style repositories as singletons? Why?

Or should I maybe use a dependency injector container to manage my repositories and decide if they are singletons or not?

I'm still reading DDD Quickly, and would like to see some good repository examples.

Answer 1

Use your dependency injection container to decide how and where repositories are created.

By using

UserRepository.Instance.Find(userId);

you're creating a barrier to testing.

If your repositories are passed into services using Constructor Injection, then you can also easily replace them with mocks.