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Code Issues 32 Releases Wiki Activity

Fixed #26500 -- Added SKIP LOCKED support to select_for_update().

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Thanks Tim for the review.
This commit is contained in:
Simon Charette
2016-06-23 11:52:14 -04:00
parent 46509cf13d
commit b8e6e1b43b
11 changed files with 98 additions and 27 deletions
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23
docs/ref/models/querysets.txt
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@@ -1528,7 +1528,7 @@ For example::
``select_for_update()``
~~~~~~~~~~~~~~~~~~~~~~~
.. method:: select_for_update(nowait=False)
.. method:: select_for_update(nowait=False, skip_locked=False)
Returns a queryset that will lock rows until the end of the transaction,
generating a ``SELECT ... FOR UPDATE`` SQL statement on supported databases.
@@ -1546,16 +1546,19 @@ selected rows, the query will block until the lock is released. If this is
not the behavior you want, call ``select_for_update(nowait=True)``. This will
make the call non-blocking. If a conflicting lock is already acquired by
another transaction, :exc:`~django.db.DatabaseError` will be raised when the
queryset is evaluated.
queryset is evaluated. You can also ignore locked rows by using
``select_for_update(skip_locked=True)`` instead. The ``nowait`` and
``skip_locked`` are mutually exclusive and attempts to call
``select_for_update()`` with both options enabled will result in a
:exc:`ValueError`.
Currently, the ``postgresql``, ``oracle``, and ``mysql`` database
backends support ``select_for_update()``. However, MySQL has no support for the
``nowait`` argument. Obviously, users of external third-party backends should
check with their backend's documentation for specifics in those cases.
backends support ``select_for_update()``. However, MySQL doesn't support the
``nowait`` and ``skip_locked`` arguments.
Passing ``nowait=True`` to ``select_for_update()`` using database backends that
do not support ``nowait``, such as MySQL, will cause a
:exc:`~django.db.DatabaseError` to be raised. This is in order to prevent code
Passing ``nowait=True`` or ``skip_locked=True`` to ``select_for_update()``
using database backends that do not support these options, such as MySQL, will
cause a :exc:`~django.db.DatabaseError` to be raised. This prevents code from
unexpectedly blocking.
Evaluating a queryset with ``select_for_update()`` in autocommit mode on
@@ -1580,6 +1583,10 @@ raised if ``select_for_update()`` is used in autocommit mode.
``select_for_update()`` you should use
:class:`~django.test.TransactionTestCase`.
.. versionchanged:: 1.11
The ``skip_locked`` argument was added.
``raw()``
~~~~~~~~~