title: How can I make a django datetime field dependent on another field?
body: <p>I have a model and modelform defined as follows</p>
  
  <pre><code>class Article(models.Model):
      is_draft = models.BooleanField(default=True)
      date_published = models.DateTimeField(editable=False, blank=True, null=True)
  
      def save(self, *args, **kwargs):
          if (self.is_draft == False) and (self.date_published == None):
              self.date_published = datetime.now()
          super().__init__(*args, **kwargs)
  
  class ArticleForm(models.ModelForm):
      class Meta:
          fields = ['is_draft']
  
      def save(self, force_insert=False, force_update=False, commit=True):
          article = Article(**self.cleaned_data)
          article.save()
  </code></pre>
  
  <p>What is strange is that when I add the custom save method to the model, the parameters for the save method from ArticleForm get passed to it. That is, force_insert=False, force_update=False are passed into the Article save method as well. Why is this happening?</p>