mirrors/django
1
0
Fork 0
mirror of https://github.com/django/django.git synced 2024-12-23 01:25:58 +00:00
Code Issues 25 Releases Wiki Activity

Fixed #23817 -- Updated docs on QuerySet evaluation

Browse Source 
Removed inaccurate info about partial evaluation after refs #18702.
Added information on modifying sliced QuerySets; refs #22503.
This commit is contained in:
Michal Petrucha 2014-11-13 19:59:00 +01:00 committed by Tim Graham
parent 788fa9fffa
commit 327df551e8
1 changed files with 6 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
docs/ref/models/querysets.txt
View File

@ -39,7 +39,12 @@ You can evaluate a ``QuerySet`` in the following ways:
``QuerySet`` usually returns another unevaluated ``QuerySet``, but Django
will execute the database query if you use the "step" parameter of slice
syntax, and will return a list. Slicing a ``QuerySet`` that has been
evaluated (partially or fully) also returns a list.
evaluated also returns a list.
Also note that even though slicing an unevaluated ``QuerySet`` returns
another unevaluated ``QuerySet``, modifying it further (e.g., adding
more filters, or modifying ordering) is not allowed, since that does not
translate well into SQL and it would not have a clear meaning either.
* **Pickling/Caching.** See the following section for details of what
is involved when `pickling QuerySets`_. The important thing for the
@ -63,11 +68,6 @@ You can evaluate a ``QuerySet`` in the following ways:
entry_list = list(Entry.objects.all())
Be warned, though, that this could have a large memory overhead, because
Django will load each element of the list into memory. In contrast,
iterating over a ``QuerySet`` will take advantage of your database to
load data and instantiate objects only as you need them.
* **bool().** Testing a ``QuerySet`` in a boolean context, such as using
``bool()``, ``or``, ``and`` or an ``if`` statement, will cause the query
to be executed. If there is at least one result, the ``QuerySet`` is