The AssertNumQueriesContext didn't reset connection's use_debug_cursor
in case there was an exception. This resulted in leaking query strings
into connection.queries. Maximum memory use pre-patch was around 700MB,
post-patch it is around 200MB for Django's test suite.
Model.save() will use UPDATE - if not updated - INSERT instead of
SELECT - if found UPDATE else INSERT. This should save a query when
updating, but will cost a little when inserting model with PK set.
Also fixed#17341 -- made sure .save() commits transactions only after
the whole model has been saved. This wasn't the case in model
inheritance situations.
The save_base implementation was refactored into multiple methods.
A typical chain for inherited save is:
save_base()
_save_parents(self)
for each parent:
_save_parents(parent)
_save_table(parent)
_save_table(self)
Thanks Anssi for haggling until I implemented this.
This change alleviates the need for atomic_if_autocommit. When
autocommit is disabled for a database, atomic will simply create and
release savepoints, and not commit anything. This honors the contract of
not doing any transaction management.
This change also makes the hack to allow using atomic within the legacy
transaction management redundant.
None of the above will work with SQLite, because of a flaw in the design
of the sqlite3 library. This is a known limitation that cannot be lifted
without unacceptable side effects eg. triggering arbitrary commits.
The sql/query.py add_q method did a lot of where/having tree hacking to
get complex queries to work correctly. The logic was refactored so that
it should be simpler to understand. The new logic should also produce
leaner WHERE conditions.
The changes cascade somewhat, as some other parts of Django (like
add_filter() and WhereNode) expect boolean trees in certain format or
they fail to work. So to fix the add_q() one must fix utils/tree.py,
some things in add_filter(), WhereNode and so on.
This commit also fixed add_filter to see negate clauses up the path.
A query like .exclude(Q(reversefk__in=a_list)) didn't work similarly to
.filter(~Q(reversefk__in=a_list)). The reason for this is that only
the immediate parent negate clauses were seen by add_filter, and thus a
tree like AND: (NOT AND: (AND: condition)) will not be handled
correctly, as there is one intermediary AND node in the tree. The
example tree is generated by .exclude(~Q(reversefk__in=a_list)).
Still, aggregation lost connectors in OR cases, and F() objects and
aggregates in same filter clause caused GROUP BY problems on some
databases.
Fixed#17600, fixed#13198, fixed#17025, fixed#17000, fixed#11293.
Before there was need to have both .relabel_aliases() and .clone() for
many structs. Now there is only relabeled_clone() for those structs
where alias is the only mutable attribute.
It isn't necessary to disable set_autocommit since its use is prohibited
inside an atomic block. It's still necessary to disable the legacy
transaction management methods for backwards compatibility, until
they're removed.
Replaced them with per-database options, for proper multi-db support.
Also toned down the recommendation to tie transactions to HTTP requests.
Thanks Jeremy for sharing his experience.
