title: Create a table in rails and add foreign key constraint
body: <p>I have a table <code>students</code> with field <code>ward_id</code> and I have to create a table named <code>guardian_users</code> with fields <code>id,ward_id</code>,<code>email</code>,<code>guardian_id</code>,<code>hashed_password</code> etc.</p>
  
  <p>Now I have to add constraint <code>foreign key</code>. Any update/delete/edit/insertion in students should have same effect on guardian_users.</p>
  
  <p>How can I do that in rails 2.3.5?</p>
  
  <p>Table students exists but other one doesn't exist yet.</p>