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Fixed #2565: added a note about the laziness of querysets in tutorial…

… 4. Thanks, Ubernostrum.

git-svn-id: bcc190cf-cafb-0310-a4f2-bffc1f526a37
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1 parent a419079 commit b97636944df970ef5d0e6bc0f691ba4011d2af3d @jacobian jacobian committed
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  1. +15 −0 docs/tutorial04.txt
15 docs/tutorial04.txt
@@ -206,6 +206,21 @@ for the polls app, we manually specify a template name for the results view:
``template_name='polls/results.html'``. Otherwise, both views would use the same
template. Note that we use ``dict()`` to return an altered dictionary in place.
+.. note:: ``all()`` is lazy
+ It might look a little frightening to see ``Poll.objects.all()`` being used
+ in a detail view which only needs one ``Poll`` object, but don't worry;
+ ``Poll.objects.all()`` is actually a special object called a ``QuerySet``,
+ which is "lazy" and doesn't hit your database until it absolutely has to. By
+ the time the database query happens, the ``object_detail`` generic view will
+ have narrowed its scope down to a single object, so the eventual query will
+ only select one row from the database.
+ If you'd like to know more about how that works, The Django database API
+ documentation `explains the lazy nature of QuerySet objects`_.
+.. _explains the lazy nature of QuerySet objects: ../db_api/#querysets-are-lazy
In previous parts of the tutorial, the templates have been provided with a context
that contains the ``poll`` and ``latest_poll_list`` context variables. However,
the generic views provide the variables ``object`` and ``object_list`` as context.

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