Add prefetch related support to RawQuerySet

[Adnan Umer]

When using custom raw SQL queries with Django ORM,

• There is no support to prefetch related models to increase performance
• Query results need to be cached manually

[Tim Graham]

Tentatively accepting, although I haven't looked into the history to understand if there's a design reason why it's not implemented. A ​post on django-users suggests that using prefetch_related_objects() (which has since been ​documented as a public API) works.

I'm unchecking "Has patch" as I don't see a patch anywhere. If there's a patch somewhere, please provide a link.

[Adnan Umer]

Here is the link to ​PR that enabled this feature.

[Дилян Палаузов]

Would you mind implementing the same for bulk_create() #28692?

[Adnan Umer]

Replying to Дилян Палаузов:

Would you mind implementing the same for bulk_create() #28692?

Once someone accept the ticket, I'll post commit solution of that. BTW you can temporarily avoid that situation this way

models = ModelA.objects.select_related('b').bulk_create([ModelA(...), ModelA(...), ModelA(...)])
from django.db.models import prefetch_related_objects
prefetch_related_objects(models, 'b')
for m in models:
        print(m.b.description)  # No more extra SELECT query here

[Simon Charette]

Unless __bool__ and __len__ support is required for prefetch_related to work they should be added/tracked in another PR/ticket.

[Adnan Umer]

Replying to Simon Charette:

Unless __bool__ and __len__ support is required for prefetch_related to work they should be added/tracked in another PR/ticket.

Got that. Moving that to separate PR.

[Adnan Umer]

Did requested changes. Requesting to review the PR again.

[Carlton Gibson]

Patch is looking good. Just needs some adjustments to the documentation changes.

[Carlton Gibson]

Replying to Adnan Umer:

Replying to Simon Charette:

Unless __bool__ and __len__ support is required for prefetch_related to work they should be added/tracked in another PR/ticket.

Got that. Moving that to separate PR.

Did that happen? (I ​can't see another PR by Adnan)

I ask because the warning in ​docs/db/sql.txt about this will also need updating:

__bool__() and __len__() are not defined in RawQuerySet, and
thus all RawQuerySet instances are considered True. The reason
these methods are not implemented in RawQuerySet is that implementing
them without internal caching would be a performance drawback and adding
such caching would be backward incompatible.

[Adnan Umer]

Replying to Carlton Gibson:

Did that happen? (I ​can't see another PR by Adnan)

I havn't yet opened any new PR for that. I was just waiting on approval/merge of my existing ticket. Once that is done I'll create a new PR for that.

I ask because the warning in ​docs/db/sql.txt about this will also need updating:

Yes, I've created #29337 and assigned that to myself. Not sure should I open PR once this one got merged or before merge

[Adnan Umer]

Unchecking "Needs Documentation" to have PR reviewed again after doing requested changes.

[Tim Graham <timograham@…>]

In 534d8d87:

Fixed #28600 -- Added prefetch_related() support to RawQuerySet.

[Дилян Палаузов]

Would you mind implementing the same for bulk_create() #28692?