#35733: Page.__len__ could skip a query if self.paginator.count == 0
-------------------------------------+-------------------------------------
Reporter: Jacob Walls | Owner: Jacob
Type: | Walls
Cleanup/optimization | Status: assigned
Component: Core (Other) | Version: dev
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Changes (by Simon Charette):
* stage: Unreviewed => Accepted
Comment:
In this case I think it's safe to move forward with the optimization, the
closest ticket I could find is #23771.
Note that a similar optimization could have done the other way around
though where when a page is requested `if len(page.object_list) <
paginator.per_page` then `count` can be deduced from `self.paginator.count
= (self.number - 1) * self.paginator.per_page + len(self.object_list)`.
{{{#!diff
diff --git a/django/core/paginator.py b/django/core/paginator.py
index 7b3189cc8b..6b0aafc6d0 100644
--- a/django/core/paginator.py
+++ b/django/core/paginator.py
@@ -89,7 +89,7 @@ def page(self, number):
number = self.validate_number(number)
bottom = (number - 1) * self.per_page
top = bottom + self.per_page
- if top + self.orphans >= self.count:
+ if self.orphans and top + self.orphans >= self.count:
top = self.count
return self._get_page(self.object_list[bottom:top], number, self)
@@ -188,7 +188,14 @@ def __repr__(self):
return "<Page %s of %s>" % (self.number,
self.paginator.num_pages)
def __len__(self):
- return len(self.object_list)
+ if (paginator_count := self.paginator.__dict__.get("count")) ==
0:
+ return 0
+ object_list_len = len(self.object_list)
+ if paginator_count is None and object_list_len <
self.paginator.per_page:
+ self.paginator.count = (
+ self.number - 1
+ ) * self.paginator.per_page + object_list_len
+ return object_list_len
def __getitem__(self, index):
if not isinstance(index, (int, slice)):
}}}
Unfortunately because `Paginator.get_page` validates against
`self.num_pages` which triggers the calculation of `self.count` this is
not feasible. On the bright side though, this means that `get_page` will
systematically trigger `self.count` calculation which strengthen the
assumption that it's safe to use directly in `Page.__len__`.
--
Ticket URL: <https://code.djangoproject.com/ticket/35733#comment:3>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
--
You received this message because you are subscribed to the Google Groups
"Django updates" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To view this discussion on the web visit
https://groups.google.com/d/msgid/django-updates/01070191c4cd9d2a-abe03ac5-1631-463e-961a-34fe31f57b81-000000%40eu-central-1.amazonses.com.
