title: django - how to save(update) datetime field to database
body: <p>I've got some problems with Django DateTimeField. I want my script to add 7 days to <em>expiration_date</em> field in database when some conditions occur.</p>
  
  <p><strong>models.py</strong></p>
  
  <pre class="lang-py prettyprint-override"><code>class TrainingPlan(models.Model):
      user = models.OneToOneField(User, on_delete='CASCADE')
      exercise_list = models.ManyToManyField(Exercise)
      expiration_date = models.DateTimeField(default=datetime.now(timezone.utc))
      reps = models.PositiveIntegerField(default=10)
  </code></pre>
  
  <p><strong>views.py</strong></p>
  
  <pre class="lang-py prettyprint-override"><code> def check_plan_expiration_date():
      user_exp_date = user_trainingplan.expiration_date
      now = datetime.now(timezone.utc)
      if user_exp_date &lt;= now:
          user_exp_date = datetime.now(timezone.utc)+timedelta(days=7)
          user_exp_date.save()
      else:
          return user_exp_date
  </code></pre>
  
  <p>Error I get:
  <strong>'datetime.datetime' object has no attribute 'save'</strong></p>