usefull scopes for Rails3

scopes.rb

#include in your model 
#include Scopes
module Scopes
  def self.included(base)
    #scope for NOT IN 
    #usage:
    #  Model.not_in(1)
    #  Model.not_in(1,2,4)
    #  Model.not_in([1,2,4])
    #  Model.not_in(1,2,3,[4,5,6])
    #  Model.not_in(Model.where(:attribute => value))
    #  Model.not_in(model_instance)
    #  Model.not_in(Model.where(:atrribute => value),model_instance)
    #  any other combinations
    base.scope :not_in, lambda { |*a| where("`#{base.name.tableize}`.`id` NOT IN (#{a.flatten.collect{|el| el.is_a?(Integer) ? el: el.id}.join(',')})") }
  end
end