This allows these tests to run on databases that reject duplicate NULL
values in unique fields e.g. SQL Server.
Forward port of 4fb50a9a from stable/1.7.x.
Regression from f51c1f59 when using select_related then prefetch_related
on the reverse side of an O2O:
Author.objects.select_related('bio').prefetch_related('bio__books')
Thanks Aymeric Augustin for the report and tests. Refs #17001.
The original patch for custom prefetches didn't allow usage of custom
queryset for single valued relations (along ForeignKey or OneToOneKey).
Allowing these enables calling performance oriented queryset methods like
select_related or defer/only.
Thanks @akaariai and @timgraham for the reviews. Refs #17001.
This patch introduces the Prefetch object which allows customizing prefetch
operations.
This enables things like filtering prefetched relations, calling select_related
from a prefetched relation, or prefetching the same relation multiple times
with different querysets.
When a Prefetch instance specifies a to_attr argument, the result is stored
in a list rather than a QuerySet. This has the fortunate consequence of being
significantly faster. The preformance improvement is due to the fact that we
save the costly creation of a QuerySet instance.
Thanks @akaariai for the original patch and @bmispelon and @timgraham
for the reviews.
Dražen Odobašić
Gagaro
Tim Graham
Jon Dufresne
Berker Peksag
Thomas Chaumeny
Aymeric Augustin
Loic Bistuer
Simon Charette
valtron
Loic Bistuer
Aymeric Augustin
Alex Gaynor
Alasdair Nicol
Claude Paroz
Luke Plant
Florian Apolloner