Question

I would like to know if this is possible to create a custom validation for my User Entity.

I Want to verify if the username is unique.
If the user Already exist, I don’t want to save it and show a warning.

I Read about Data Annotation inherits but I’m not sure of what I’m doing.

Please help.

Thanks.

Entity-Framework 4
Asp.net MVC 2

Answer 1

Yes it is possible, you can create your own Custom Attribute class and validate the entity. Something similar to this code,

    [AttributeUsage(AttributeTargets.Class)]
    public class DuplicateUserAttribute : ValidationAttribute
    {
    private const string _defaultErrorMessage = "user '{0}' Already exist";

    public DuplicateUserAttribute ()
        : base(_defaultErrorMessage)
    {
    }

    public override string FormatErrorMessage(string name)
    {
        return String.Format(CultureInfo.CurrentUICulture, ErrorMessageString);

    }

    public override bool IsValid(object value)
    {
        UserEntity NewUser = value as UserEntity;
        //Write here logic to validate the user is already exist in database like
        context.UserList.Where(u=>u.Name ==NewUser .UserName)
        return ;
    }
}

[DuplicateUser]
Class User
{
 …
}

Also more on CustomeAttribute