Django excluding one queryset from another

Question

I have the following two models:

class DeliveryTime(models.Model):    delivery_time = models.CharField(max_length=15)  class BlockedDeliveryTime(models.Model):    delivery_date = models.DateField()    delivery_time = models.ForeignKey(DeliveryTime)  

I want to return all the available delivery times for a day i.e. all DeliveryTime excluding the BlockedDeliveryTime.

 blocked_delivery_times = BlockedDeliveryTime.objects.filter(delivery_date=delivery_date)  delivery_times = DeliveryTime.objects.all() 

From delivery_times queryset I want to remove all blocked_delivery_times.delivery_time

How can I do that? Any suggestions?

Answer 1

blocked_delivery_times = BlockedDeliveryTime.objects.filter(delivery_date=delivery_date) \     .values('delivery‌​_time') delivery_times = DeliveryTime.objects.exclude(id__in=blocked_delivery_times) 

Answer 2

With the release of Django 1.11 you can use difference, which takes advantage of the EXCEPT SQL operator. I think it might be more efficient because you aren't evaluating a query to get a list of values.