Accessing custom helper methods in rails 3 migrations - ruby-on-rails-3

Question

In rails 2 I had a lib/migration_helpers.rb file with methods for setting and dropping foreign keys in the db.
These methods were available in self.up and self.down in migration files by adding in the migration file
require 'migration_helpers'
at the top, and
extend MigrationHelpers
immediately after the class statement.
In rails 3 this does not work, and if i try to run a migration using set_foreign_key method from migration_helpers.rb the following error is thrown:
== AddFkToArticles: migrating ================================================
-- set_foreign_key("articles", "book_id", "books")
rake aborted!
An error has occurred, this and all later migrations canceled:
undefined method `set_foreign_key' for #<AddFkToArticles:0x000001034a1f38>
Tasks: TOP => db:migrate
(See full trace by running task with --trace)
I already checked that in config/application.rb the autoload path is set to include lib.
The file is effectively required, because if i comment out the require statement then rails whines about the missing 'migration_helpers' file.
I suspect this is a scoping problem (rails 2 used "def self.up", rails 3 uses "def change")
but cannot imagine how to solve the problem (by now I simply copied the code in the migration file, just to check that it does what it should do).
Francesco

Answer 1

I don't know what exactly you're trying to accomplish but here's some code that might give you a clue.
## lib/test_helper.rb
module TestHelper
def my_table_name
return :mytable
end
end
And then the migration:
## db/migrate/test_migration.rb
include TestHelper
class TestMigration < ActiveRecord::Migration
def self.up
create_table my_table_name
end
def self.down
drop_table my_table_name
end
end
Including this helper inside the Migration class doesn't work so it should be outside.