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Fixed #17001 -- Custom querysets for prefetch_related.

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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.
This commit is contained in:
Loic Bistuer
2013-11-07 00:25:05 +07:00
committed by Anssi Kääriäinen
parent b1b04df065
commit f51c1f5900
9 changed files with 616 additions and 65 deletions
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15
docs/releases/1.7.txt
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@@ -98,6 +98,21 @@ Using a custom manager when traversing reverse relations
It is now possible to :ref:`specify a custom manager
<using-custom-reverse-manager>` when traversing a reverse relationship.
New ``Prefetch`` object for advanced ``prefetch_related`` operations.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The new :class:`~django.db.models.Prefetch` object allows customizing
prefetch operations.
You can specify the ``QuerySet`` used to traverse a given relation
or customize the storage location of prefetch results.
This enables things like filtering prefetched relations, calling
:meth:`~django.db.models.query.QuerySet.select_related()` from a prefetched
relation, or prefetching the same relation multiple times with different
querysets. See :meth:`~django.db.models.query.QuerySet.prefetch_related()`
for more details.
Admin shortcuts support time zones
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