title: Adding foreign keys in Rails 3.2
body: <p>I've just inherited a blog platform that uses Rails 3.2 (!!), and I'm looking to add some functionality. I have two models, <code>Article</code> and <code>Issue</code>, which I'd like to associate such that any <code>Issue</code> <code>has_many :articles</code> and and any <code>Article</code> <code>belongs_to :issue</code>.</p>
  
  <p>I've looked into using the gem <code>foreigner</code> to help with this, but I'm wondering if there's a way to do this without adding more gems. I've looked around SO and seen some conflicting stuff. <a href="https://stackoverflow.com/questions/20041474/add-has-many-and-belongs-to-migration-from-command-line">This SO post</a> seems to only apply to Rails 4, which I guess automatically generates this sort of migration.</p>
  
  <p>Can I do this manually by migrating to create appropriate integer fields in both schemas, and then putting the <code>has_many</code> and <code>belong_to</code> statements in the models?</p>
  
  <p>Thanks so much!</p>