title: How to autopopulate new field in models' existing objects with unique values in Django?
body: <p>I have added new field called slug which need to be unique. It is already existing project.</p>
  
  <p>During migrations Django asks what value should be used to fill already created objects. However any string will cause a conflict as value will not be unique.</p>
  
  <p>I was planning to fill the slug field with values from other field of this model namely username.</p>
  
  <p>Question: How can I populate above slug field (with unique = True) during migrations with unique values. Or maybe there is another way around that.</p>
  
  <p>Thanks</p>