Repository Pattern - Validating Object and Return Message

Question

I'm working on a website, and just trying to get my head around the general structure. I have a database in the background that I'm accessing using the "Repository Pattern". I have the below code in my UserRepository class:

public bool IsValid(User user)
{
  if (_context.Users.Any(c => c.EmailAddress == user.EmailAddress))
  {
    Message = "Email address already in use";
    return false;
  }

  return true;
}

And that is implemented here

[HttpPost]
[AllowAnonymous]
[ValidateAntiForgeryToken]
public ActionResult Register(User user)
{
  if (ModelState.IsValid)
  {
    var context = new Context("DatabaseContext");
    var userRepo = new UserRepository(context);

    if (userRepo.IsValid(user))
    {
      userRepo.Add(user);
      // return to different view
    }
    else
    {
      // display userRepo.Message on page
      return View(user);
    }
  }

  return View(user);
}

My problem is I don't think I'm going around the "message" bit correctly, but I can't find anything online to help me out (specifically around repository). I think I should be changing the return type of IsValid to something like a result (as I've seen with dialog boxes), but again, I'm not sure.

Any help would be much appreciated.

Thanks.

Answer 1

One way to achieve this is exactly like you have suggested - change the return type of IsValid.

In the past I have had similar validation methods in my "business layer" that return a collection of ValidationResult, where each returned record accounts for a validation error within the model and an empty collection would be interpreted as a valid model.

For example:

public class ValidationResult
{
    public string FieldName { get; set; }
    public string Message { get; set; }
}

public interface IValidator<T>
{
    IEnumerable<ValidationResult> IsValid(T model);
}

//...in your implementation
public IEnumerable<ValidationResult> IsValid(User user)
{
    //Return a new ValidationResult per validation error
    if (_context.Users.Any(c => c.EmailAddress == user.EmailAddress))
    {
        yield return new ValidationResult
        {
            Message = "Email address already in use",
            FieldName = nameof(user.EmailAddress)
        };
    }
}

This could then be interpreted by your presentation layer to feedback to the user.

Answer 2

I agree with what you mentioned in question. Returning custom class will be better approach IMO.

public ValidationResult IsValid(User user)
{
  ValidationResult validationResult = new ValidationResult(true, "");
  if (_context.Users.Any(c => c.EmailAddress == user.EmailAddress))
  {
    validationResult.Status = false;
    validationResult.Message = "Email address already in use";
    return validationResult;
  }

  return validationResult;
}

This way, Status and Message give you all info needed. Check the status first. If it is false, check message for exact details.