title: Django - MySQL database datetime field gets cleared
body: <p>When I save a value for datetime through a POST request, it gets saved in the database (I verify by logging the value by quering for it afterwards). But when I reload my page, the value is set to 0000-00-00 00:00:00</p>
  
  <pre><code># models.py
  class Assignment(models.Model):   
    temp = models.CharField(max_length = 32)
    deadline = models.DateTimeField(default=lambda: datetime.datetime.now() + datetime.timedelta(days=14))
  
  # views.py
  def some_function(request):
    deadline = request.POST['deadline']
    assignment.deadline = datetime.timedelta(int(deadline)) + datetime.datetime.now()
  </code></pre>
  
  <p>When I log the assignment.deadline value throughout this function, it's always what I expect it to be (the current date + whatever the value in the POST request was).
  However, when the page reloads, the value is set back to 0000-00-00 00:00:00</p>
  
  <p>Why is this happening?</p>