Conditionally required property using data annotations

Question

I have a class like this:

public class Document
{
   public int DocumentType{get;set;}

   [Required]
   public string Name{get;set;}

   [Required]
   public string Name2{get;set;}
}

Now if I put a [Required] data annotation on the Name and Name2 properties, then everything is ok and if Name or Name2 are empty, validation will throw an error.

But I want Name field only to be required if DocumentType is equal to 1 and Name2 only required if DocumentType is equal to 2 .

public class Document
{
   public int DocumentType{get;set;}

   [Required(Expression<Func<object, bool>>)]
   public string Name{get;set;}

   [Required(Expression<Func<object, bool>>)]
   public string Name2{get;set;}
}

but I know I can't, it causes an error. What should I do for this requirement?

Answer 1

Out of the box I think this is still not possible.

But I found this promising article about Mvc.ValidationToolkit (also here, unfortunately this is only alpha, but you probably could also just extract the method(s) you need from this code and integrate it on your own), it contains the nice sounding attribute RequiredIf which seems to match exactly your cause:

• you download the project from the linked zip and build it
• get the built dll from your build folder and reference it in the project you are using
• unfortunately this seems to require reference to MVC, too (easiest way to have that is starting an MVC-Project in VS or install-package Microsoft.AspNet.Mvc)
• in the files where you want to use it, you add using Mvc.ValidationToolkit;
• then you are able to write things like [RequiredIf("DocumentType", 2)] or [RequiredIf("DocumentType", 1)], so objects are valid if neither name or name2 are supplied as long as DocumentType is not equal to 1 or 2