mass_habtm.rb

class << Foo
  def mass_habtm(attr_array)
    attr_str = attr_array.map{|a| %Q{'#{a}'} }.uniq.join(",")
    self.connection.execute(%Q{insert into foos_bars (foo_id,bar_id) 
                     select distinct foos.id,bars.id from foos,bars 
                     where foos.id = #{self.id} 
                     and bars.some_attribute in (#{attr_str})})
  end
end