Rails: How to add add_index to existing table
The self.up method is correct. Use this for your self.down:
remove_index :units, :column => :lesson_id
Almost
class AddIndexToUnits < ActiveRecord::Migration def self.up add_index :units, :lesson_id, :name=>'lesson_index' end def self.down remove_index :units, 'lesson_index' endend
To remove an index, you must use remove_index with the same table and column specification as the self.up's add_index has. So:
def self.down remove_index :units, :lesson_idendA multi-column index example would be:
def self.down remove_index :units, [:lesson_id, :user_id]end