Hi,
I got somewhat stuck on progress with this ticket, and as I'd like to
get it merged eventually (and avoid an abundant amount of fixes), I have
a few things I like a bit of input about.
1. Since this is specific to postgres, I'm looking for a better place to
put the actual Window-expression class, as well as axillary helpers
(Order By, Partition and the frame).
django/db/models/sql/expressions.sql may be one such place, but perhaps
introducing another file for this? Eventually, something like WITHIN
GROUP could be added, which shares some traits with window expressions.
This also goes the tests.
2. Tests, and if the initial test-cases seem fair? I took a small sample
of test cases related to some made-up salaries in a few departments. I
tried to introduce some wrapper to guard against testing functions that
aren't available (Oracle is the most complete in this sense, PostgreSQL
doesn't support all of the aggregate-functions, such as Variance).
3. The Order By-clause proposed in the initial code in the code only
leaves room for one column (no expressions). A regular query has
"add_ordering" to add more than one ordering-clause to a query, but this
just works for an ordering in SELECT, and I didn't spot anything that
could be used for this. Maybe abstracting the code from add_ordering so
it could be used also for something more? Something similar goes for
Partition By. Again, I'm sure it's a common use case to partition and
order by more than one expression. I currently commented out the
OrderByWrapper.
4. Would it be ok to add code for this in the base backend? I'm thinking
of constants for CURRENT ROW etc. which are shared among backends. I had
a look at SQLalchemy to see how things are arranged there, and what it
supports. SQLalchemy is feature-rich, but leaves out more
expressive-style ranges, and only supports unpreceding following/current
row, unbound following. I guess this is a reasonable limitation to make.
5. Will a 2.0 release notes be introduced soon, as I'm certain I won't
manage to make the final PR before the 1.11 feature freeze as it needs
to be finished, reviewed and merged. I started some time ago, and had it
lying around till I understood window functions better.
As pointed out in #26608, I have some rough, drafty code that's quite
far from a PR. I'm more interested in input for the above.
I'm relatively new to Django internals (it's fun and educational hacking
on them), and it took me some time to read through the code and
documentation for the ORM, and there are many facets of it I can still
understand. If someone is willing to guide me a bit, I'd be quite
helpful. Thank you.
--
Med venlig hilsen / Kind regards,
Mads Jensen
Saajan Fernandes: I think we forget things if there is nobody to
tell them.
-- The Lunchbox (2013)
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