gistfile1.txt

class Person < ActiveRecord::Base
  named_scope :job, lambda { |name|
    { :joins => :job, :conditions => { "job.name" => name } }
  }
  named_scope :car, lambda { |number|
    { :joins => :car, :conditions => { "car.number" => number } }
  }
end

gistfile2.txt

person = Person.job('Task').car(23)