#35733: Page.__len__ could skip a query if self.paginator.count == 0
-------------------------------------+-------------------------------------
Reporter: Jacob | Owner: Jacob Walls
Walls |
Type: | Status: assigned
Cleanup/optimization |
Component: Core | Version: dev
(Other) |
Severity: Normal | Keywords:
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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With code like this,
{{{
paginator = Paginator(unevaluated_queryset, 25)
page = paginator.get_page(1) # causes count query via validate_number()
if not page: # causes select query
return {}
}}}
I get an additional query versus:
{{{
paginator = Paginator(unevaluated_queryset, 25)
if not paginator.count: # causes count query
return {}
}}}
----
In the case of no data, the second SELECT query is unnecessary if we
already know the paginator is empty. Since `paginator.count` is cached,
would it be worth optimizing out this additional query? Otherwise, you
have to dig into the internals to discover that the two examples above do
not perform equivalently.
{{{#!diff
diff --git a/django/core/paginator.py b/django/core/paginator.py
index 7b3189cc8b..334166636d 100644
--- a/django/core/paginator.py
+++ b/django/core/paginator.py
@@ -188,6 +188,8 @@ class Page(collections.abc.Sequence):
return "<Page %s of %s>" % (self.number,
self.paginator.num_pages)
def __len__(self):
+ if self.paginator.count == 0:
+ return 0
return len(self.object_list)
def __getitem__(self, index):
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/35733>
Django <https://code.djangoproject.com/>
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