C# Data Annotations in Interface

Question

Quick question...

If I put a notation in the Interface...

Say [Required]

can I ommit that notation in the C# class for the property?

i.e. can I...

Interface IFoo
{
   [Required]
   string Bar {get; set;}
}

Class Foo : IFoo
{
   string Bar {get; set;}
}

or do I need to just not put the notation in the interface and do this...

Interface IFoo
{
   string Bar {get; set;}
}

Class Foo : IFoo
{
   [Required]
   string Bar {get; set;}
}

Answer 1

Placing the Data Annotation in the interface won't work. In the following link there is an explanation as to why: http://social.msdn.microsoft.com/Forums/en-US/adonetefx/thread/1748587a-f13c-4dd7-9fec-c8d57014632c/

A simple explanation can be found by modifying your code as follows:

interface IFoo
{
   [Required]
   string Bar { get; set; }
}

interface IBar
{
   string Bar { get; set; }
}

class Foo : IFoo, IBar
{
   public string Bar { get; set; }
}

Then it is not clear as to whether the Bar string is required or not, since it is valid to implement more than one interface.

Answer 2

The Data Annotation won't work but I don't know why.

If you are using EF code first you can use Fluent API to force this behavior when creating your database. This is a workaround, not a real solution because only your database will check the constraint, not EF or any other system working with Data Annotation (well I suppose).

I did it with

public partial class MyDbContext : DbContext
{
    // ... code ...

    protected override void OnModelCreating(DbModelBuilder dbModelBuilder)
    {
        dbModelBuilder.Types<IFoo>().Configure(y => y.Property(e => e.Bar).IsRequired());
    }
}

Telling the system that when it recognize a class implementing IFoo you configure the property to IsRequired.