This is a cool feature.<p>Unfortunately, when I looked into this for our codebase, I found that it doesn't have full support in Rails 3. You can make the index, via a migration, but rails won't include it properly in your `schema.rb` file. So restoring via schema (as opposed to running through all your migrations from scratch) or just trying to understand your database by looking at schema.rb won't give you a full picture.<p>However, looking at `add_index` in rails 4, it seems to support it!<p>edit: one thing I did try out was you can change your schema file from `schema.rb` to `schema.sql`, which supposedly fixes it, but I had some issues with that which I don't remember at the moment.