How to keep your MVC controllers DRY for Edit->Save->ValidateFail

Question

I've got a Manage User event that takes an an optional userID and displays a user edit screen. There is a manageUserViewModel to go with this screen.

My Manage page has some dependencies - eg, PageTitle, what method to submit to, etc.

If I validate-fail, I need to show the manage screen again, but this time, using the view-model that was passed into the same method.

Supplying these dependencies in the fail scenario isn't very DRY.

How do I step repeating the dependencies? I tried putting them into a separate method, but that does not feel right.

public ActionResult Manage(Guid? UserID)
    {
        User user = this._UserLogic.GetUser(UserID);

        ViewBag.Title = "User List";
        ViewBag.OnSubmit = "Save";
        ManageUserViewModel uvm = Mapper.Map<User, ManageUserViewModel>(user);

        return View("Manage", uvm);
    }


    [AcceptVerbs("POST")]
    public ActionResult Save(ManageUserViewModel uvm)
    {
        User user = this._UserLogic.GetUser(uvm.UserID);


        if (!ModelState.IsValid)

            // This is not very DRY!!!
            ViewBag.Title = "Manage User";
            ViewBag.OnSubmit = "Save";
            return View("Manage", uvm);
        }

        Mapper.Map<ManageUserViewModel, User>(uvm, user );

        this._UserLogic.SaveUser(user);

        return RedirectToAction("Manage", new { UserID = user.ID });

    }

Answer 1

I think you misunderstand DRY. DRY does not mean "NEVER repeat yourself", it means that you should not repeat yourself when it makes sense not to.

Different views have different requirements, and creating a complex structure just to avoid repeating yourself violates other best practices, like KISS, and SRP.

SOLID is interesting because Single Responsibility Principle is often at odds with Don't Repeat Yourself, and you have to come up with a balance. In most cases, DRY loses because SRP is far more important.

It looks to me like you have code here that is handling multiple responsibilities just so you can avoid writing similar code more than once. I disagree with doing that, because each view has different responsibilities and different requirements.

I would suggest just creating separate controller actions, views, and models for each action, particularly if the validation requirements are different for them. There may be a few things you can do (like using Partial Views or Editor Templates) to reduce repetition, but in general don't add lots of complexity just to avoid repetition.