A model class with a LINQ Expression

Author.cs

public class Author
{
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public Membership Membership { get; set; }

    public static Expression<Func<Author, bool>> GoldAndUp = x =>
            x.Membership == Membership.Gold || x.Membership == Membership.Platinum;
}