Validating uniqueness with data annotations in asp.net mvc - asp.net

Question

I have various questions about validation using data annotations. I am using the following setup
asp.net mvc 2
entity framework 4
data annotations
Basically, I'm trying to get unique validation working and i'm a little confused. My models are as follows:
public class Buyer
{
public int Id { get; set; }
[Required(ErrorMessage = "The email is required")]
public string Email { get; set; }
[Required(ErrorMessage= "The name is required")]
public string Name { get; set; }
}
public class Seller
{
public int Id { get; set; }
[Required(ErrorMessage = "The email is required")]
public string Email { get; set; }
[Required(ErrorMessage= "The name is required")]
public string Name { get; set; }
}
I have set up a unique field attribute as follows
public class UniqueFieldAttribute : ValidationAttribute
{
public IUniqueValidator Validator { get; set; }
public int Id { get; set; }
public override bool IsValid(object value)
{
if (value == null)
{
return true;
}
return Validator.IsValid(Convert.ToString(value), Id);
}
}
I then created a validator that implements the IUniqueValidator interface:
public class BuyerUniqueEmailValidator : IUniqueValidator
{
public bool IsValid(string value, int id)
{
TheDb db = new TheDb();
var existing = from Buyer b in db.Buyers
where b.Email.ToLower() == value.ToLower()
select b;
foreach (Buyer b in existing)
{
if (b.Id != id)
{
return false;
}
}
return true;
}
}
The idea is there! However, on execution I am having problems. When I add this
[UniqueField(Validator=new BuyerUniqueEmailValidator(), Id=this.Id ErrorMessage= "This email is in use")]
the project won't compile.
Basically, what I want to know is if it is possible to pass a class to the validationAttribute to perform the validation? Also, how can i pass an id.
Additionally, is there anyway to create a generic unique field generator that would work for all my models that have an email field, or do I have to have a BuyerEmailValidator, a SellerEmailValidator etc, etc. I can't seem to get T working correctly.
Only worried about serverside at the moment.
Thanks

Answer 1

Your code implementation of this can't see any records not visible to its own transaction, and, hence, can't work reliably in a multi-user environment. Why not use a DB constraint?