OrderBy takes an expression - it doesn't have to be a single column. For
example, this is valid:
(Lower('last_name') + Lower('first_name)).desc() ==
OrderBy(Lower('last_name') + Lower('first_name), descending=True)
On Friday, 25 November 2016 23:22:58 UTC+11, Mads Jensen wrote:
>
> On Tuesday, November 22, 2016 at 11:50:17 PM UTC+1, Josh Smeaton wrote:
>
>> Thanks for picking this up. I've been wondering if Window expressions
>> would be possible, and what limitations we might have to make based on our
>> ORM.
>>
>
> I was fortunate that the reporter posted a snippet to work from :)
> Django's ORM is quite flexible, and adaptable. I remember seeing a video
> with Alex Gaynor where he complained about its shortcomings, but that
> seemed to have been sorted out.
>
> https://www.youtube.com/watch?v=GxL9MnWlCwo
>
>
>> > 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).
>>
>> I would create a new file beside expressions.py called
>> django/db/models/window.py.
>>
>>
> Seems like a good starting point. I have been contemplating that
> grouping.py could be a good name as well, in case somehow would like to add
> WITHIN GROUP, or support for grouping sets (a bigger fish, since that means
> appending stuff after GROUP BY etc.)
> Anyway, I have some window.py locally.
>
>
>> > 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.
>>
>> Yes, it's a good start, but I haven't thoroughly reviewed them yet
>> either. It'll be easier to do when there's a proper PR.
>>
>
> I wouldn't call it proper, but I posted a pull request, and marked it
> [WIP].
>
> > 3. The Order By-clause proposed in the initial code in the code only
>> leaves room for one column (no expressions).
>>
>> Wouldn't the existing OrderBy type be sufficient? Really though,
>> windowing should support a list of expressions (then call asc() or desc()
>> on them).
>>
>
> Maybe I'm reading the code wrong, but doesn't OrderBy just refer to a
> column, or are types of Expression/ExpressionWrapper also valid input?
>
>
>> > 4. Would it be ok to add code for this in the base backend?
>>
>> Yes, if it makes the implementation nicer/easier for django and 3rd party
>> backends. If having the code in the backend prevents *users* from creating
>> their own windowing functions or modifying existing ones, then that's
>> probably not ok. Django, backends, and users all need to be able to
>> construct their own windowing expressions. You can certainly share code in
>> the backend though, with things like PRECEDING ROW etc.
>>
>
> I'm cleaning up things in the pull request. At least elements that are
> mandatory are there, such as docs, tests and some code.
>
>
>> > 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.
>>
>> None of us understand all of the ORM, and we're more than happy to have
>> more people helping out, so thanks! If you create a PR (even if it's not
>> ready, just mark is [WIP] for Work In Progress) it'll be easier to comment
>> on specific things within the code and see all of the commits tied
>> together. You're also more likely to get feedback on a PR and some guidance
>> there too.
>>
>
> Good. I tend to have several small things in my commits, but I'll try to
> work on individual things in this PR.
>
> Thanks for input.
>
> Kind regards,
> Mads
>
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