title: Saving form data rewrites the same row
body: <p>i can't figure out how to save my form data creating a new row, when saving it just rewrites the data using the same 'id' and trhows me an error when there are multiple rows, this is my code:</p>
  
  <p><b> models.py:</b></p>
  
  <pre>
  class Submitter(models.Model):
      submitter=models.ForeignKey(User)
  
      def __unicode__(self):
          return self.submitter.username
  
  class Store(models.Model):
      creator=models.ForeignKey(Submitter)
      name = models.CharField(_('name'),blank=True,max_length=30)
      st = models.CharField(_('Street'),blank=True,max_length=30)
      sub_date = models.DateField(_('Visit Date'),)
  
      def __str__(self):
          return u'%s-%s-%s'%(self.creator,self.name,self.sub_date)
  </pre>
  
  <p><b> views.py:</b></p>
  
  <pre>
  def StoreSave(request):    
      if request.method == 'POST':
          form = StoreForm(request.POST)
          if form.is_valid():
              submitter, dummy= Creator.objects.get_or_create(creator=request.user)
              store, created = Store.objects.get_or_create(
                  submitter=submitter
              )
              store.name = form.cleaned_data['name']
              store.st = form.cleaned_data['st']
              store.visit_date = form.cleaned_data['visit_date']
              store.save()
              return HttpResponseRedirect('/user/%s/' % request.user.username)
      else:
          form = StoreForm()
      variables = RequestContext(request, {
              'form': form
      })
      return render_to_response('store/create_store.html', variables)</pre>