Issues using another app's database structure

[dgets]

Not sure how to fix this, I'm beyond the tutorial that I was using now... Anyway I'm trying to record the administration of a substance (by its id field), within the 'usage' or 'administration' record that I'm creating. Not quite sure how to get this laid out so Django will be happy with it:

class Usage(models.Model):
    sub = models.ForeignKey(Substance)
    dosage = models.IntegerField()
    timestamp = models.DateTimeField('time administered', default=timezone.now)
    notes = models.CharField(max_length=160)

[dgets]

The way to do this is 'appname.Tablename', so it would be sub = models.ForeignKey('subadd.Substance') in the previous code snippet.