Changing a non-primary-key column to a Rails-standard `id` primary key column, and back down again

gistfile1.rb

  def up
    rename_column :table_name, :old_id_col, :id
    change_column :table_name, :id, :primary_key
  end

  def down
    rename_column :table_name, :id, :old_id_col
    change_column :table_name, :old_id_col, :integer, :null => true
    remove_column :table_name, :id
  end

Given a table with no primary key set, change the name of the column, then set that column as the primary key. Tricky part here is migrating down, where we have to rename the column to be the old column name, change that column to be an int with :null => true, then remove the id column, because for some reason the rename column isn't removing that ID column