Question

I am working on an application and trying to follow Robert C. Martin’s SOLID principles. I am using the Command Pattern and I was wondering about the implementation. In all of his examples in Clean Code and Agile Principles, Patterns and Practices in C# his command objects never return anything. His Command interface is;

public interface Command
{
  void Execute();
}

All of the examples are “AddEmployee”, “DelEmployee”, “EditEmployee”, etc. Would I have a command that would be “GetAllEmployees” or is there some other special “Interactor” I would create for that specific purpose? One way I am thinking of handling that specific case is to have two interfaces a non generic like the one above and a generic one like this;

public interface Command<T>
{
  T Execute();
}

What I am asking is would this be an acceptable implementation of this pattern or is there another way we would access data from the application?

Answer 1

A command is something that changes state (updates, deletes or additions).

When getting data (and not changing it), you would use a query.

Also see CQS and the related CQRS.