gistfile1.rb

class AddSequenceToTableName < ActiveRecord::Migration
def up
    #add sequence to 
    execute <<-SQL
  ALTER TABLE table_name ALTER COLUMN id SET DEFAULT nextval('table_name_id_seq'::regclass);
    SQL
  end
 
  def down
	execute <<-SQL
		ALTER TABLE table_name ALTER COLUMN id SET NOT NULL;
	SQL
  end
end