ASP.NET MVC ViewModels polymorphism

Question

Folks, I have architectural question:

I have several viewmodels of very similar looking items, with different data annotations:

public class VM1 {
  [Display(Name="VM1 Field1")]
  public string Field1 { get; set; }
  [Display(Name="VM1 Field2")]
  public string Field2 { get; set; }
}
public class VM2 {
  [Display(Name="VM2 Field1")]
  public string Field1 { get; set; }
  [Display(Name="VM2 Field2")]
  public string Field2 { get; set; }
}
public class VM3 {
  [Display(Name="VM3 Field1")]
  public string Field1 { get; set; }
  [Display(Name="VM3 Field2")]
  public string Field2 { get; set; }
}

Is there a way for me to define one abstract class VMBase so that VM1/2/3 will inherit and how to assign the data annotation in that case? Basically class-wise its typical polymorphic situation, but data annotation - don't know how to handle those in this case?

Also how views needs to look so they will show proper class? Or will I have to multiply the entire thing 3 times (potentially the list will grow) just for data annotation sake?

If you think it can be done easier with fluent validation - please provide example (viewmodel, controller, view)

Edit But I am trying to stick with Data Annotations: those are for view models, while fluent validation is more for domain entities. I need client side validation that is coming from data annotation out of the box, and isn't from fluent validation.

Thank you in advance.

Your edit is completely wrong. Fluent Validation is great for validation of your view models because it is a lot more flexible than Data Annotations. What you have in your example; however, is only for metadata on the Html Helpers, which FV is not intended to replace. — Dismissile
– Dismissile, Commented Feb 27, 2013 at 20:50
@Dismissile My ignorance. This is precisely why I am asking. Thanks for the info! Testing the fluent validation with client side. Once done I'll be back here. Thanks folks! — Display Name
– Display Name, Commented Feb 27, 2013 at 23:00
Personally, I love Data Annotations. You can see at a glance what you expect a property to do and how it should behave. Unfortunately, as soon as you throw in inheritance, they're essentially worthless and only cause problems. I wish the MVC/EF teams would find a way to overload them, but not really even sure if that is possible, since it would likely mean using something like Fluent API (which you might as well just use FluentValidation, then) or it would require redefining the property, which negates the benefits of inheritance. Oh well. — Chris Pratt
– Chris Pratt, Commented Feb 28, 2013 at 14:45

Chris Pratt · Accepted Answer · 2013-02-27 19:41:51Z

1

I've had this same problem. However, I think I might have found a solution in FluentValidation. It's like the Fluent API for EF, if you've ever used that, but covers the validation facets that Fluent API doesn't, without having to resort to Data Annotations, which as you mention, makes it impossible to compose classes if the validation for a particular property will be different somewhere in the inheritance chain.

answered Feb 27, 2013 at 19:41

Chris Pratt

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2 Comments

Display Name Over a year ago

My problem with fluent validation is that it doesn't give me client side validation out of the box, which is extremely easily achieved with data annotation.

Erik Funkenbusch Over a year ago

@DisplayName - Fluent Validation does give client-side validation with common types. The list of client-side support is here: fluentvalidation.codeplex.com/…

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