I was looking at the repository method for an ASP.NET MVC app and noticed a static class wasn't used.
Since the repo is CRUD, why not make it static?
1) It's difficult to do unit testing with static classes (if you are testing a class that depends on your repository, you want that test to work against a fake 'mocked' repository object instead of your real one)
2) You often want to have 1 repository instance per-request to make it easier to ensure that uncommited changes from one user don't mess things up for another user.
Repository pattern increase testability, static classed decreases it.
来源：https://stackoverflow.com/questions/5622592/why-arent-data-repositories-static