redmine/db/migrate/20130201184705_add_unique_index_on_tokens_value.rb

class AddUniqueIndexOnTokensValue < ActiveRecord::Migration[4.2]
  def up
    say_with_time "Adding unique index on tokens, this may take some time..." do
      # Just in case
      duplicates = Token.connection.select_values("SELECT value FROM #{Token.table_name} GROUP BY value HAVING COUNT(id) > 1")
      Token.where(:value => duplicates).delete_all

      add_index :tokens, :value, :unique => true, :name => 'tokens_value'
    end
  end

  def down
    remove_index :tokens, :name => 'tokens_value'
  end
end