How to use Dependency Injection with Static Methods?

Question

Imagine there is a Customer class with an instance Load() method.

When the Load() method is called, it retrieves order details

Answer 1

If you must keep the static method, I would wrap the static calls in a Repository object.

Like this:

interface IOrderRepository {
   IEnumerable GetAll(customerId, ..);
}

class OrderRepository : IOrderRepository {
   IEnumerable GetAll(customerId, ...)
   {
     Order.GetAll(customerId,...); // The original static call.
   }
}

Now you inject this repository into your Customer class.

(I'm assuming you're doing this so you can inject fake IOrders at runtime for testing purposes. I should say that in general, static methods are a serious obstacle to testing.)