title: Django model with unique_together and without auto incremented id primary key
body: <p>So I have a Django model that stores 5 days worth of data in it because the amount of data is so large we must delete all data older than 5 days. The model currently has the auto incremented id field that Django creates automatically. The problem here is that pretty soon it won't be able to generate primary keys large enough. </p>
  
  <p>Ideally, I'd have a composite primary key, but Django doesn't support this yet. So I was looking at unique_together and wondering if it was possible to just use that as a pesudo pk and remove the auto incrementing id because its not really used for anything in the application.</p>
  
  <p>Another option is this module: <a href="https://github.com/simone/django-compositekey" rel="nofollow">django-compositekey</a> but I'm not to sure how well its supported?</p>
  
  <p>In either case the I would need to combine 4 columns to make a unique record:</p>
  
  <pre><code>class MassObservations(models.Model):
      time = models.DateTimeField()
      star = models.ForeignKey('Stars')
      property = models.ForeignKey('Properties')
  
      observatories = (('1', 'London'),
                       ('2', 'China'),
                       ('3', 'United States'))
  
      station = models.CharField(max_length=2, choices=observatories)
      mass = models.FloatField()
  
      class Meta:
          unique_together = ('time', 'star', 'property', 'station')
  </code></pre>
  
  <p>Any other ideas on how to treat data/Django table like this?</p>