title: How to add relation beeween two models
body: <p>I have these models on Rails :</p>
  
  <pre><code>class Tweet &lt; ActiveRecord::Base
    attr_accessible :status
    belongs_to :user
  end
  
  class User &lt; ActiveRecord::Base
    attr_accessible :name
    has_many :tweets
  end
  </code></pre>
  
  <p>but on bd there isn't a relationship between these models.
  Which migration i need to do for add user_id into tweet table?</p>