From 327df551e89a505c5756becee97c40198f38aff2 Mon Sep 17 00:00:00 2001 From: Michal Petrucha Date: Thu, 13 Nov 2014 19:59:00 +0100 Subject: [PATCH] Fixed #23817 -- Updated docs on QuerySet evaluation Removed inaccurate info about partial evaluation after refs #18702. Added information on modifying sliced QuerySets; refs #22503. --- docs/ref/models/querysets.txt | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/docs/ref/models/querysets.txt b/docs/ref/models/querysets.txt index 1cf215bc465..2bd24357cfe 100644 --- a/docs/ref/models/querysets.txt +++ b/docs/ref/models/querysets.txt @@ -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