title: Django model validate date and datetime ranges
body: <p>What is the best solution to validate a date and dateTime interval in a Django model?</p>
  
  <p>This is my model:</p>
  
  <pre><code>class PriceOption(Model):
      from_datetime = DateTimeField(verbose_name=_('from datetime'))
      to_datetime = DateTimeField(verbose_name=_('to datetime'))
  
      from_time = TimeField(verbose_name=_('from time'))
      to_time = TimeField(verbose_name=_('to time'))
  </code></pre>
  
  <p>And I need to make sure that from_datetime happens before to_datetime and the same for from_time and to_time. </p>
  
  <p>Should I override the save method? Or validators somehow?</p>
  
  <p>I see that Postgres have Date and DateTime range fields. This would only solve the first pair of fields.</p>