title: Ruby On Rails custom ID
body: <p>Hi I want to have custom ids for a table and not use the default auto_increment. Is that possible? I have turned :id => false and later on I create a t.column :id, :bigint
  But when I create a new record the id is set to NULL</p>
  
  <p>Is there anyway to bypass this behaviour.
  I could set my primary key to a field uid (it is actually facebook id) but usually it breaks for me as relations usually look for the id field</p>