Rails - Jun 2006 - migration to be called inside others migrations

Hi list

I''m writing some migrations to move a legacy db on a rails app. I have
a bunch of tables which need some custom modifications and the columns
updated_at to be added etc...

Now since the rails related columns will be the same for many (but not
all) tables I was thinking... can I write a Migration that sounds like
that

class AddRailsFields < ActiveRecord::Migration

  def self.up(tbname)
    add_column tbname, "lock_version", :integer, :default => 0
    rename_column tbname, "oldtimestamp", "updated_at"
  end

  def self.down(tbname)
    remove_column tbname, "lock_version"
    rename_column tbname, "updated_at", "oldtimestamp"
  end

end

And call it inside other migrations as

AddRailsFields.up("tablename")

I''ve tried this but AddRailsFields (which is located in dedicated file
in db/migrations/) seems to be not defined in other migrations. Maybe
a ''require'' in the right place could fix the problem, but I
would
avoid to add the require to each migration or to put it in some place
too generic.

Thanks for any help

Paolo