efficient filter objects in django based on other tables objects

Question

I have two models in django and I want to remove all objects from one table, that match a subset of the other tables params. My Question now is, what is the most efficient way.

The a is around 5000 objects, while b is around 40000 objects.

My current solution looks like this, but that doesn't feel right.

a_with_a_and_b = a.objects.filter(param1='a', param2='b').values('c','d')

for a in a_with_a_and_b:
    _b = b.filter(param3=a['c'],param4=a['d'])
    if _b:
        print('delete it')

4140tm · Accepted Answer · 2020-02-10 08:57:56Z

1

How about something like this:

list_c = a.objects.filter(param1='a', param2='b').values_list('c', flat=True)
list_d = a.objects.filter(param1='a', param2='b').values_list('d', flat=True)

b.objects.filter(param3__in=list_c, param4__in=list_d).delete()

answered Feb 10, 2020 at 8:57

4140tm

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2 Comments

Flo Over a year ago

I need an exact combination of d and c. the __in would combine all possibilities, right? I.e. if a are names like john doe and paul rich it would find the name paul doe in b, right?

4140tm Over a year ago

The end result would be identical to your example. It's the same filtering criteria for a and the resulting to sequences would contain the same values as in the dicts when using .values('c','d'). By using __in you just offload the iteration to the database.

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