Reusing named_scope to define another named_scope

Answer 1

You can use a method to combine some named_scope like :

def self.from_big_guys
  self.class.user_group_managers_salary_greater_than(100)
end

This feature is add on Rails 3 with new syntax (http://m.onkey.org/2010/1/22/active-record-query-interface)

Answer 2

Refer to this question raised time ago here at SO. There is a patch at lighthouse to achieve your requirement.

Answer 3

You can use proxy_options to recycle one named_scope into another:

class Thing
  #...
  named_scope :billable_by, lambda{|user| {:conditions => {:billable_id => user.id } } }
  named_scope :billable_by_tom, lambda{ self.billable_by(User.find_by_name('Tom').id).proxy_options }
  #...
end

This way it can be chained with other named_scopes.

I use this in my code and it works perfectly.

I hope it helps.