Specification

Specification.markdown

First of all, here’s something you can do with the Specification class to reduce some of the code you have to write. Add the following methods:

public AndSpecification<TEntity> And(Expression<Func<TEntity, bool>> second)
{
    return new AndSpecification<TEntity>(this, new Specification<TEntity>(second));
}

public OrSpecification<TEntity> Or(Expression<Func<TEntity, bool>> second)
{
    return new OrSpecification<TEntity>(this, new Specification<TEntity>(second));
}

This allows you to write this:

IEnumerable<Product> products = repository.Find<Product>(
    new Specification<Product>(p => p.Price < 100).Or(p => p.Name == "Windows XP Professional"));

I think it looks nicer. Anyway, for your question I would recommend you to subclass Specification:

public class EmailExistsSpecification : Specification<Email>
{
    public EmailExistsSpecification(string email)
        : base(e => e.Email.ToUpper() == email.ToUpper())
    {
    }
}

Now you can re-use the EmailExistsSpecification in your methods. Nice huh?