title: How to change primary ID of a record in Rails?
body: <pre>
  rails console
  u = User.find(9)
  u.id = 7 # There is no other record with id 7
  u.save
  => true
  User.all
  </pre>
  
  <p>The id has not changed.</p>
  
  <p>How to change the primary ID? Why does it prevent this action?</p>
  
  <p>Working in Rails 3.0.7 and PostgreSQL.</p>
  
  <p>EDIT:
  Since there are good reasons not to do this, I'll explain why and hopefully it is a good reason.</p>
  
  <p>We are doing Usability Testing on Staging, so I want it to look like the Production to make it easy for everyone. I don't want to create confusion or errors in the Usability Testing process by having some things in one order on Staging and in a different order on Production. I only changed one PK id on Staging DB.</p>
  
  <p>Don't do this on your production DB!</p>