title: Empty Scope with Ruby on Rails
body: <p>Following Problem:<br />
  I need something like an empty scope. Which means that this scope is emtpy, but responds to all methods a scope usually responds to.
  I'm currently using a little dirty hack. I simply supply "1=0" as conditions. I find this realy ugly, since it hits the database. Simply returning an empty array won't work, since the result must respond to the scoped methods.</p>
  
  <p>Is there a better existing solution for this or will I need to code this myself?</p>
  
  <p>Maybe some example code could help explain what i need:</p>
  
  <pre><code>
  class User &lt; ActiveRecord::Base
    named_scope :admins, :conditions => {:admin => true }
    named_scope :none_dirty, :conditions => "1=0" # this scope is always empty
  
    def none_broken
      []
    end
  
    def self.sum_score # okay, a bit simple, but a method like this should work!
      total = 0
      self.all.each do |user|
        total += user.score
      end
      return total
    end
  end
  User.admin.sum_score # the score i want to know
  User.none_drity.sum_score # works, but hits the db
  User.none_broken.sum_score # ...error, since it doesn't respond to sum_score
  </code></pre>