Hello,
Thanks for the link :)
I think the documentation would be better structured, then, if
https://docs.djangoproject.com/fr/4.0/ref/models/querysets/ would
reference your link.
I have not read all of Django documentation.
I do not know if it is expected that most developers would read everything.
Hence, I learn using Google top ranked pages inside Django
documentation when I search for a narrow topic on Django.
If I search
django prefetch
django prefetching
django prefetch_related
django prefetch_related_objets
I have https://docs.djangoproject.com/fr/4.0/ref/models/querysets/ as
first result but your link does not appear.
If I search
django cache
django caching
I get this
https://docs.djangoproject.com/fr/4.0/topics/cache/
but also your link as the third answer of Google.
Maybe, adding a link to /topics/db/optimization from
ref/models/querysets/ would help Google and people like me find this
information more easily :)
Best regards,
Laurent Lyaudet
Le ven. 24 juin 2022 à 08:05, Jason a écrit :
>
>
> This is explicitly called out in the documentation at
> https://docs.djangoproject.com/en/4.0/topics/db/optimization/#understand-queryset-evaluation
> On Thursday, June 23, 2022 at 1:17:50 PM UTC-4 laurent...@gmail.com wrote:
>>
>> Hello,
>>
>> I made a simple test to check the number of queries done :
>>
>> # First part
>> order = Order.objects.get(id=2) # one query
>> items = list(order.items.all()) # one query
>> items = list(order.items.all()) # one query
>> items = list(order.items.all()) # one query
>>
>> # Second part
>> order = Order.objects.prefetch_related("items").get(id=2) # two queries
>> items = list(order.items.all()) # no query
>> items = list(order.items.all()) # no query
>> items = list(order.items.all()) # no query
>>
>> # Third part
>> order = Order.objects.get(id=2) # one query
>> prefetch_related_objects([order], "items") # one query
>> items = list(order.items.all()) # no query
>> items = list(order.items.all()) # no query
>> items = list(order.items.all()) # no query
>> prefetch_related_objects([order], "items") # no more query
>> prefetch_related_objects([order], "items") # no more query
>>
>> I was surprised that there was 4 queries for the First part of the test
>> instead of 2 for the other parts, because I was expecting that .all() would
>> also fill the cache and not only use it.
>> Maybe it is intended.
>> I think that this test or something else explaining this point could enhance
>> the documentation on prefetch_related() and prefetch_related_objects().
>> I advised my colleagues to use prefetch_related_objects() when in doubt
>> whether the objects given have been already extended with prefetching.
>>
>> Best regards,
>> Laurent Lyaudet
>>
>>
>>
>>
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