1λ rake db:find_indexes
 2
 3* TIP: if you have a problem with the index name('index name too long') you can solve with the :name option. Something like :name => 'my_index'.
 4* run `rails g migration AddMissingIndexes` and add the following content:
 5
 6
 7    class AddMissingIndexes < ActiveRecord::Migration
 8      def change
 9        add_index :cakes, :user_id
10      end
11    end