title: Change boolean value for user object
body: <p>I want to be able to change my "sendmail" boolean value for a user via my view. But after adding the object once for a user with the value True I can't change it anymore because I get an "IntegrityError at /accounts/send_me_email/ column user_id is not unique". What am I doing wrong?</p>
  
  <pre>
  models.py
  
  class SendMeMail(models.Model):
      user = models.ForeignKey(User, unique=True)
      sendmail = models.BooleanField()
  </pre>
  
  <pre>
  views.py
  
  from userprofile.models import SendMeMail
  def send_me_email(request):
      """
      Define if a user want email notifications or not
      """
  
      # Check for current sendmail value and act accordingly
      sendme = SendMeMail(user=request.user)
  
      if sendme.sendmail == False:
          sendme.sendmail = True
          sendme.save()
      if sendme.sendmail == True:
          sendme.sendmail = False
          sendme.save()
      else:
          sendme.sendmail = True
          sendme.save()
  </pre>