title: Django filter query on with property fields automatically calculated
body: <p>There is Django Order model with property fields automatically calucated. How to do a filter query.</p>
  
  <pre><code>class Order(models.Model):
  
      @property
      def expire(self):
          return self.created + datetime.timedelta(days=self.days_left())
  
      @property
      def days_left(self):
          return self.recurrence_period  * self._recurrence_unit_days[self.recurrence_unit]
  </code></pre>
  
  <p>Calculation done to get 1,3,7 datetime days from today</p>
  
  <pre><code>settings.SUBSCRIPTION_EXPIRATION_REMIND = [1, 3, 7]
  
  days = map(lambda x: datetime.date.today() + datetime.timedelta(days=x), settings.SUBSCRIPTION_EXPIRATION_REMIND)
  
  [datetime.date(2015, 7, 28),
   datetime.date(2015, 7, 30),
   datetime.date(2015, 8, 3)]
  </code></pre>
  
  <p>How to filter by ORM query </p>
  
  <pre><code>Order.objects.filter(expire__in=days)
  </code></pre>
  
  <p>Django is throwing error.</p>
  
  <pre><code>FieldError: Cannot resolve keyword 'expire' into field.
  </code></pre>