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Diffstat (limited to 'docs')
| -rw-r--r-- | docs/ref/models/querysets.txt | 2 | ||||
| -rw-r--r-- | docs/releases/1.7.txt | 26 |
2 files changed, 28 insertions, 0 deletions
diff --git a/docs/ref/models/querysets.txt b/docs/ref/models/querysets.txt index 834b849c8f..fa4a09756f 100644 --- a/docs/ref/models/querysets.txt +++ b/docs/ref/models/querysets.txt @@ -2132,6 +2132,8 @@ extract two field values, where only one is expected:: inner_qs = Blog.objects.filter(name__contains='Ch').values('name', 'id') entries = Entry.objects.filter(blog__name__in=inner_qs) +.. _nested-queries-performance: + .. admonition:: Performance considerations Be cautious about using nested queries and understand your database diff --git a/docs/releases/1.7.txt b/docs/releases/1.7.txt index 4999fc11a8..a453301999 100644 --- a/docs/releases/1.7.txt +++ b/docs/releases/1.7.txt @@ -574,6 +574,32 @@ a :exc:`~exceptions.ValueError` when encountering them, you will have to install pytz_. You may be affected by this problem if you use Django's time zone-related date formats or :mod:`django.contrib.syndication`. +``remove()`` and ``clear()`` methods of related managers +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +The ``remove()`` and ``clear()`` methods of the related managers created by +``ForeignKey``, ``GenericForeignKey``, and ``ManyToManyField`` suffered from a +number of issues. Some operations ran multiple data modifying queries without +wrapping them in a transaction, and some operations didn't respect default +filtering when it was present (i.e. when the default manager on the related +model implemented a custom ``get_queryset()``). + +Fixing the issues introduced some backward incompatible changes: + +- The default implementation of ``remove()`` for ``ForeignKey`` related managers + changed from a series of ``Model.save()`` calls to a single + ``QuerySet.update()`` call. The change means that ``pre_save`` and + ``post_save`` signals aren't sent anymore. + +- The ``remove()`` and ``clear()`` methods for ``GenericForeignKey`` related + managers now perform bulk delete. The ``Model.delete()`` method isn't called + on each instance anymore. + +- The ``remove()`` and ``clear()`` methods for ``ManyToManyField`` related + managers perform nested queries when filtering is involved, which may or + may not be an issue depending on your database and your data itself. + See :ref:`this note <nested-queries-performance>` for more details. + .. _pytz: https://pypi.python.org/pypi/pytz/ Miscellaneous |