bidirectional-migrations.rb

# old style
class AddUserToUploadedFiles < ActiveRecord::Migration
  def self.up
    add_column :uploaded_files, :user_id, :integer
  end

  def self.down
    remove_column :uploaded_files, :user_id
  end
end

# new even better style
class AMigration < ActiveRecord::Migration
  def self.up
    add_column :uploaded_files, :user_id, :integer
  end
end

AMigration.migrate(:up) # add column
AMigration.migrate(:down) # remove column - this is generated automagically

# more complex
class ASlightlyComplexMigration < ActiveRecord::Migration
  def self.up
    create_table :users do |t|
      t.string :username, :null => false
      t.string :name, :null => false
    end
    add_index :users, :username, :unique => true
  end
end

ASlightlyComplexMigration.migrate(:up) # create table, add_index
ASlightlyComplexMigration.migrate(:down) # drop_index, drop_table - generated automatically


# drop table
class DropMigration < ActiveRecord::Migration
  def self.down
    create_table :users do |t|
      t.string :username, :null => false
      t.string :name, :null => false
    end
  end
end

DropMigration.migrate(:up) # drop_table - generated automatically
DropMigration.migrate(:down) # create_table