:has_one and migrating production data base

I am leery of migrating my perfectly stable and fine production data

But I need to add some customer info to my system.

I am adding a new model backed by a database for the new customer
Thus I'm assuming that I won't need to migrate the old database. The
change is
that there is a new database.

However the existing production database will need a ':has_one' for
the new

This is the change I need to make to the production database of
The new database will hold download links and passwords, for some
orders, So I need the new database (Order_Download) to contain the
above fields (download_link and password) plus the foreign key
order_id, and the old database (Orders)
will contain an ':has_one' to associate it with Order_Download.

So I have:

class Order < ActiveRecord::Base
  has_one: order_download // NEW, ADDING TO PRODUCTION DATABASE

class OrderDownload < ActiveRecord::Base // new database
  belongs_to :order

The question is, can I just add this and nothing will break, nothing
migrating, everything is cool?

Or am I changing the production database Orders with a new ':has_one'
is going to require me to do something painful? Like migrate, yuck.

Sorry I'm a database newbie and I'd rather not mess with it.

I am still something of a newbie myself, but as I read the documentation (I wish I could give you a better link than "http://api.rubyonrails.org/, search for “belongs_to” 6 times), the model with the foreign key is the one that “belongs_to” the the model that “has_one” of the other model. See the section entitled “Is it a belongs_to or has_one association?”

Keeping in mind that I too am a newbie, I don’t think you will have to touch your existing database, (although you will want to modify your model with the “has_one” attribute if you want to reach the corresponding entry in the new table.

Of course, you can (and should) copy your existing production database to your development database and verify that none of your changes affect the existing database.