Rails: Changing relationship after initial migration

I am having some trouble finding a good answer to my question on rails relationship creation.

If I already ran the initial migration for my user model and my comment model Without declaring a relationship (ie: a user has_many comments, and comments belong_to user) how do I define that relationship later on?

Can I simply: 1-add the user_id column to Comments, 2-declare the relationship and 3-run the new add_user_id_to_comm开发者_StackOverflow社区ent migration file?

Will this work? If not, how would I go about changing the relationship after already having ran the initial migration for the models? Thank you so much for your help.\

Rails 3.1, Ruby 1.8.7

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You can just add the reference in another migration, using the change_table migration (documentation):

change_table :comments do |t|
  t.references :user
end

Then just add the associations to your models.

class User < ActiveRecord::Base
  has_many :comments
end

class Comment < ActiveRecord::Base
  belongs_to :user
end