Models that use SET, SET_NULL, and SET_DEFAULT as on_delete handler
don't have to fetch objects for the sole purpose of passing them back to
a follow up UPDATE query filtered by the retrieved objects primary key.
This was achieved by flagging SET handlers as _lazy_ and having the
collector logic defer object collections until the last minute. This
should ensure that the rare cases where custom on_delete handlers are
defined remain uncalled when when dealing with an empty collection of
instances.
This reduces the number queries required to apply SET handlers from
2 to 1 where the remaining UPDATE use the same predicate as the non
removed SELECT query.
In a lot of ways this is similar to the fast-delete optimization that
was added in #18676 but for updates this time. The conditions only
happen to be simpler in this case because SET handlers are always
terminal. They never cascade to more deletes that can be combined.
Thanks Renan GEHAN for the report.
This has been supported for subqueries wrapped in Subquery since the expression
was introduced and for Queryset directly since Subquery resolves to sql.Query.
Piggy-backed on the existing tests covering Coalesce handling of EmptyResultSet
as it seemed like a proper location to combine testing.
Adds support for joint predicates against window annotations through
subquery wrapping while maintaining errors for disjointed filter
attempts.
The "qualify" wording was used to refer to predicates against window
annotations as it's the name of a specialized Snowflake extension to
SQL that is to window functions what HAVING is to aggregates.
While not complete the implementation should cover most of the common
use cases for filtering against window functions without requiring
the complex subquery pushdown and predicate re-aliasing machinery to
deal with disjointed predicates against columns, aggregates, and window
functions.
A complete disjointed filtering implementation should likely be
deferred until proper QUALIFY support lands or the ORM gains a proper
subquery pushdown interface.
Node.create() which has a compatible signature with Node.__init__()
takes in a single `children` argument rather than relying in unpacking
*args in Q.__init__() which calls Node.__init__().
In addition, we were often needing to unpack iterables into *args and
can instead pass a list direct to Node.create().
Node._new_instance() was added in
6dd2b5468f to work around Q.__init__()
having an incompatible signature with Node.__init__().
It was intended as a hook that could be overridden if subclasses needed
to change the behaviour of instantiation of their specialised form of
Node. In practice this doesn't ever seem to have been used for this
purpose and there are very few calls to Node._new_instance() with other
code, e.g. Node.__deepcopy__() calling Node and overriding __class__ as
required.
Rename this to Node.create() to make it a more "official" piece of
private API that we can use to simplify a lot of other areas internally.
The docstring and nearby comment have been reworded to read more
clearly.
The tests for creating new instances or copying instances of Node and
its subclasses didn't fully capture the behaviour of the implementation,
particularly around whether the `children` list or is contents were the
same as the source.
Mohamed Karam
David Wobrock
Simon Charette
Iuri de Silvio
Neeraj Kumar
Willem Van Onsem
Claude Paroz
Mariusz Felisiak
Tom Carrick
Benoît Vinot
Haolun Chai
Carlton Gibson
David Sanders
Kamil Turek
Fiza Ashraf
Fab
Alberto Planas
Marcelo Galigniana
Nick Pope