There's no reason to disable fast-delete when an intermediary
many-to-many model has connected m2m_changed receivers because the
signal is only sent when related manager's clear() and remove() methods
are directly called.
This must have been overlooked in 1cd6e04cd4
given no regression tests fail when m2m_changed is not taken into
consideration to determine if fast-delete can be enabled.
Checked the following locations:
* Model.save(): If there are parents involved, take the safe way and use
transactions since this should be an all or nothing operation.
If the model has no parents:
* Signals are executed before and after the previous existing
transaction -- they were never been part of the transaction.
* if `force_insert` is set then only one query is executed -> atomic
by definition and no transaction needed.
* same applies to `force_update`.
* If a primary key is set and no `force_*` is set Django will try an
UPDATE and if that returns zero rows it tries an INSERT. The first
case is completly save (single query). In the second case a
transaction should not produce different results since the update
query is basically a no-op then (might miss something though).
* QuerySet.update(): no signals issued, single query -> no transaction
needed.
* Model/Collector.delete(): This one is fun due to the fact that is
does many things at once.
Most importantly though: It does send signals as part of the
transaction, so for maximum backwards compatibility we need to be
conservative.
To ensure maximum compatibility the transaction here is removed only
if the following holds true:
* A single instance is being deleted.
* There are no signal handlers attached to that instance.
* There are no deletions/updates to cascade.
* There are no parents which also need deletion.
The only reason why GenericForeignKey and GenericRelation are stored
separately inside _meta is that they need to be cloned for every model
subclass, but that's not true for any other virtual field. Actually,
it's only true for GenericRelation.
Field.rel is now deprecated. Rel objects have now also remote_field
attribute. This means that self == self.remote_field.remote_field.
In addition, made the Rel objects a bit more like Field objects. Still,
marked ManyToManyFields as null=True.
SQLite doesn't work with more than 1000 parameters in a single query.
The deletion code could generate queries that try to get related
objects for more than 1000 objects thus breaking the limit. Django now
splits the related object fetching into batches with at most 1000
parameters.
The tests and patch include some work done by Trac alias NiGhTTraX in
ticket #21205.
Since "unless managed" now means "if database-level autocommit",
committing or rolling back doesn't have any effect.
Restored transactional integrity in a few places that relied on
automatically-started transactions with a transitory API.
enter_transaction_management() was nearly always followed by managed().
In three places it wasn't, but they will all be refactored eventually.
The "forced" keyword argument avoids introducing behavior changes until
then.
This is mostly backwards-compatible, except, of course, for managed
itself. There's a minor difference in _enter_transaction_management:
the top self.transaction_state now contains the new 'managed' state
rather than the previous one. Django doesn't access
self.transaction_state in _enter_transaction_management.
In a normal relational construct, if you're listening for an event
that signals a child was deleted, you dont expect that the parent
was deleted already.
This change ensures that post_delete signals are fired immediately
after objects are deleted in the graph.
Objects can be fast-path deleted if there are no signals, and there are
no further cascades. If fast-path is taken, the objects do not need to
be loaded into memory before deletion.
Thanks to Jeremy Dunck, Simon Charette and Alex Gaynor for reviewing
the patch.
Simon Charette
Florian Apolloner
Nick Pope
Étienne Loks
Дилян Палаузов
Tim Graham
Anton Samarchyan
chillaranand
Simon Charette
Claude Paroz
Michal Petrucha
Laura Feier
sarthakmeh
Maxime Lorant
Alexander Sosnovskiy
Anssi Kääriäinen
Andriy Sokolovskiy
Loic Bistuer
Daniel Pyrathon
Thomas Chaumeny
Anssi Kääriäinen
Gavin Wahl
Aymeric Augustin
Rodolfo Carvalho
Christopher Medrela
Loic Bistuer
Curtis Maloney
David Cramer
Alex Gaynor
Alex Gaynor