a) Maybe its an option to put the foreign key to the other model? This way 
you dont need to make a join to find out if there is a relation.

b) Save the existing ralation status to model A

c) cache the A.objects.filter(bs__isnull=False) query

But apart from that i fear you cannot do much more, since this is just a DB 
and not a Django ORM question.

Am Freitag, 2. Februar 2018 14:47:45 UTC+1 schrieb Web Architect:
> Hi,
> I am trying to optimise Django queries on my ecommerce website. One of the 
> fundamental query is where I have no clue how to make efficient. It could 
> be trivial and probably been known long time back. But I am new to Django 
> and would appreciate any help. This is primarily for one to many or many to 
> many relations.
> Following is an example scenario:
> (Please pardon my syntax as I want to put across the concept and not the 
> exact django code unless it's really needed):
> Model A:
> class A(models.Model):
>     # Fields of model A
> Model B (which is related to A with foreign key):
> class B(models.Model):
>     a = models.ForeignKey('A', related_name='bs')
> Now I would like to find out all As for which there is atleast one b. The 
> only way I know is as follows:
> A.objects.filter(bs__isnull=False)
> But the above isn't an optimal way as with large of records in A and B, 
> the above takes lot of time. It gets more inefficient if it's a many to 
> many relationship.
> Could anyone please let me know the most efficient way to use django 
> queryset for the above scenario?
> Thanks.

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