title: How to add association to relations, that are already created , through migration?
body: <p>I have created 2 table <code>students</code> and <code>issued_books</code>. but forgot to add <code>t.belongs_to :students</code> in migration, while creating <code>issued_books</code> table.</p>
  
  <p>Now I have modified the corresponding model as:</p>
  
  <pre><code>class Student &lt; ActiveRecord::Base
  has_many :issued_book
  end
  
  class IssuedBook &lt; ActiveRecord::Base
  belongs_to :student
  end
  </code></pre>
  
  <p>How would I do it now through migration in rails?</p>