trjhtr

I'm trying to implement business logic layer based on concepts of commands and command handlers.

A command is a thing that contains input parameters for executing some action, and it knows what kind of output that action should produce. A command handler contains logic for actually executing an action: it accepts a command as a param, handles it in some way, and (if successful) produces an output object.

public interface ICommand<TResultData>
 

public interface ICommandHandler<TCommand, TResultData>
 where TCommand : ICommand<TResultData>
 
 CommandResult<TResultData> Handle(TCommand command);


public static class CommandProcessor

 public static CommandResult<TResultData> Process<TCommand, TResultData>(TCommand command)
 where TCommand : ICommand<TResultData>
 
 var handler = ServiceLocator.GetInstance<ICommandHandler<TCommand, TResultData>>();
 return handler.Handle(command);
 

public class CommandResult<TResultData>

 public bool Success get; set; 

 public string Error get; set; 

 public TResultData Data get; set; 

Example usage:

// CreateUserCommand & handler implementations *very* simplified
public class CreateUserCommand : ICommand<User>

 public string Email get; set; 


public class CreateUserCommandHandler : ICommandHandler<CreateUserCommand, User>

 private readonly IRepository repository;
 public CreateUserCommandHandler (IRepository repository)
 
 this.repository = repository;
 
 public CommandResult<User> Handle(CreateUserCommand command)
 
 if(this.repository.Users.Any(u=>u.Email == command.Email)
 return new CommandResult<User> Success = false, Error = "Email already taken";
 var user = new User Email = command.Email;
 this.repository.Users.Add(user);
 return new CommandResult<User> Success = true, Data = user;
 


// command usage in application code
var command = new CreateUserCommand Email = "some.email.com" ;
CommandResult<User> result = CommandProcessor.Process(command);
if(result.Success)

 // at this point we know that result.Data is of type User, which is nice
 // so we can use this strictly-typed result data in any way
 User createdUser = result.Data;
 Console.Writeline("Created user with Id = " + createdUser.Id);

else

 Console.Writeline("Error creating user: " + result.Error);

Everything works pretty nice, as you can see in the usage example, but one thing that bothers me is the empty interface ICommand. Is it a bad thing here? Can the code be refactored in some way to make it better?