Index: django/db/models/sql/query.py =================================================================== --- django/db/models/sql/query.py (revision 7513) +++ django/db/models/sql/query.py (working copy) @@ -67,6 +67,8 @@ self.order_by = [] self.low_mark, self.high_mark = 0, None # Used for offset/limit self.distinct = False + self.select_for_update = False + self.select_for_update_nowait = False self.select_related = False self.related_select_cols = [] @@ -173,6 +175,8 @@ obj.order_by = self.order_by[:] obj.low_mark, obj.high_mark = self.low_mark, self.high_mark obj.distinct = self.distinct + obj.select_for_update = self.select_for_update + obj.select_for_update_nowait = self.select_for_update_nowait obj.select_related = self.select_related obj.related_select_cols = [] obj.max_depth = self.max_depth @@ -211,6 +215,7 @@ obj = self.clone() obj.clear_ordering(True) obj.clear_limits() + obj.select_for_update = False obj.select_related = False obj.related_select_cols = [] obj.related_select_fields = [] @@ -290,6 +295,9 @@ result.append('LIMIT %d' % val) result.append('OFFSET %d' % self.low_mark) + if self.select_for_update: + result.append("%s" % self.connection.ops.for_update_sql(nowait=self.select_for_update_nowait)) + params.extend(self.extra_params) return ' '.join(result), tuple(params) Index: django/db/models/manager.py =================================================================== --- django/db/models/manager.py (revision 7513) +++ django/db/models/manager.py (working copy) @@ -108,6 +108,9 @@ def order_by(self, *args, **kwargs): return self.get_query_set().order_by(*args, **kwargs) + def select_for_update(self, *args, **kwargs): + return self.get_query_set().select_for_update(*args, **kwargs) + def select_related(self, *args, **kwargs): return self.get_query_set().select_related(*args, **kwargs) Index: django/db/models/query.py =================================================================== --- django/db/models/query.py (revision 7513) +++ django/db/models/query.py (working copy) @@ -267,6 +267,7 @@ del_query = self._clone() # Disable non-supported fields. + del_query.query.select_for_update = False del_query.query.select_related = False del_query.query.clear_ordering() @@ -402,6 +403,18 @@ else: return self._filter_or_exclude(None, **filter_obj) + def select_for_update(self, **kwargs): + """ + Returns a new QuerySet instance that will select objects with a + FOR UPDATE lock. + """ + # Default to false for nowait + nowait = kwargs.pop('nowait', False) + obj = self._clone() + obj.query.select_for_update = True + obj.query.select_for_update_nowait = nowait + return obj + def select_related(self, *fields, **kwargs): """ Returns a new QuerySet instance that will select related objects. If Index: django/db/backends/sqlite3/base.py =================================================================== --- django/db/backends/sqlite3/base.py (revision 7513) +++ django/db/backends/sqlite3/base.py (working copy) @@ -52,6 +52,10 @@ # function django_date_trunc that's registered in connect(). return 'django_date_trunc("%s", %s)' % (lookup_type.lower(), field_name) + def for_update_sql(self): + # sqlite does not support FOR UPDATE + return '' + def drop_foreignkey_sql(self): return "" @@ -171,3 +175,4 @@ return bool(re.search(re_pattern, re_string)) except: return False + Index: django/db/backends/mysql/base.py =================================================================== --- django/db/backends/mysql/base.py (revision 7513) +++ django/db/backends/mysql/base.py (working copy) @@ -89,6 +89,16 @@ def fulltext_search_sql(self, field_name): return 'MATCH (%s) AGAINST (%%s IN BOOLEAN MODE)' % field_name + def for_update_sql(self, nowait=False): + """ + Return FOR UPDATE SQL clause to lock row for update + + Currently mysql ignores NOWAIT + """ + if nowait: + raise NotImplementedError("NOWAIT option for SELECT ... FOR UPDATE not implemented with mysql"); + BaseDatabaseWrapper.for_update_sql(self,nowait=False) + def limit_offset_sql(self, limit, offset=None): # 'LIMIT 20,40' sql = "LIMIT " Index: django/db/backends/__init__.py =================================================================== --- django/db/backends/__init__.py (revision 7513) +++ django/db/backends/__init__.py (working copy) @@ -160,6 +160,16 @@ """ return cursor.lastrowid + def for_update_sql(self, nowait=False): + """ + Return FOR UPDATE SQL clause to lock row for update + """ + if nowait: + nowaitstr = ' NOWAIT' + else: + nowaitstr = '' + return 'FOR UPDATE' + nowaitstr + def limit_offset_sql(self, limit, offset=None): """ Returns a LIMIT/OFFSET SQL clause, given a limit and optional offset. Index: tests/regressiontests/queries/models.py =================================================================== --- tests/regressiontests/queries/models.py (revision 7513) +++ tests/regressiontests/queries/models.py (working copy) @@ -695,6 +695,20 @@ >>> Item.objects.exclude(~Q(tags__name='t1', name='one'), name='two') [, , ] +Bug #2075 +Added FOR UPDATE functionality +>>> from django.db import transaction +>>> @transaction.commit_manually +>>> def test_for_update(): +>>> t = Tag(name='for update test') +>>> t.save() +>>> transaction.commit() +>>> tfound = Tag.objects.select_for_update().get(pk=t.id) +>>> tfound.name = 'for update test 2' +>>> tfound.save() +>>> transaction.commit() +>>> test_for_update() + Bug #7095 Updates that are filtered on the model being updated are somewhat tricky to get in MySQL. This exercises that case. Index: docs/db-api.txt =================================================================== --- docs/db-api.txt (revision 7513) +++ docs/db-api.txt (working copy) @@ -1046,6 +1046,36 @@ ``extra()`` is new. Previously, you could attempt to pass parameters for ``select`` in the ``params`` argument, but it worked very unreliably. +select_for_update +~~~~~~~~~~~~~~~~~ + +**New in Django development version:** + +Lock rows returned from a query. Most databases allow you to exclusively +lock rows with ``select_for_update()``. To do this call the method +``select_for_update()`` to lock all retrieved objects:: + + entry = Entry.objects.select_for_update().get(pk=1) + ... + entry.save() + +All objects returned using ``select_for_update()`` will be locked with an +exclusive lock which will remain locked until the transaction has finished. +In the case of using middleware, the locks will be released when the view +returns and the transaction is committed or rolled back. SQLite does not +support an exclusive lock so this is simply ignored for SQLite. Other +databases issue a ``FOR UPDATE``. + +If you would not like to wait for the lock then set the parameter nowait to +True. In this case, it will grab the lock if it isn't already locked. If +it is locked then it will throw an exception. This is not supported +with mysql. Doing this with mysql will raise a ``NotImplemented`` exception. + +Note that all rows returned are locked. If you retrieve multiple objects, +all objects will be locked until the transaction is committed. Another +process which does a ``select_for_update()`` on the same rows will wait until +the transaction which has the locks is finished. + QuerySet methods that do not return QuerySets ---------------------------------------------