Hi Josh,
With a suitably-defined Month function your example could be:
sales_per_month = Model.objects.annotate(month=Month(F('mydate'))).values(
'month').Aggregate(sales=Sum('sale'))
ISTM there's a bit of overlap between Func and Transform that could be
cleared up - I'll start a new thread about it.
Cheers,
Alex
On Wednesday, March 25, 2015 at 12:24:44 PM UTC+8, Josh Smeaton wrote:
>
> Hi,
>
> Firstly (and least importantly) opening a PR makes it a lot easier to
> review code, especially when there are lots of commits. A [WIP] pull
> request is common and useful. If you get a chance, you should open one with
> this change.
>
> I think it's a good idea. So much so that I opened a ticket about a year
> ago: https://code.djangoproject.com/ticket/22394. You'll note some
> comments there about retaining the Year based behaviour as a `BETWEEN X and
> Y` rather than `Extract(YEAR)`. Otherwise, I think the support is rather
> positive. At a high level, your code looks fairly solid and I think would
> be a useful addition.
>
> Another thing I would really like to see is transform based annotations.
> I'm not 100% sure on whether .annotate(F('X__transform')) is supported or
> not, but if it is, we'll get some really nice behaviour from the use of
> transforms.
>
> Think:
>
> sales_per_month = Model.objects.annotate(month=F('mydate__month')).values(
> 'month').Aggregate(sales=Sum('sale'))
>
> If Transforms don't yet work with annotate, that'll probably be what I'd
> like to implement next. But the first step is having transforms to work
> with, where date based transforms are (to me) the most useful.
>
> Cheers,
>
> On Wednesday, 25 March 2015 13:39:39 UTC+11, Jon Dufresne wrote:
>>
>> Hi,
>>
>> I have been spending some time learning and investigating the custom
>> lookups feature that was newly introduced in 1.7 [0]. While
>> investigating, I wanted to learn by example so I started looking
>> through the Django code. In the end, I didn't find many examples.
>> However, I did notice that there exists lookups for the year, month,
>> day, (and more) value from a database date or datetime value [1].
>> These appear to be implemented as special case "builtin" lookups and
>> not through the new lookup mechanism. Is there a specific reason for
>> this or is it historical momentum?
>>
>> I started investigating if these could be refactored to use the common
>> code path and implemented using the new lookup mechanism. To my
>> delight it was not very difficult and I now have all tests passing
>> after refactoring these lookups. Right now, this lives in a branch of
>> mine and not in a ticket or pull request. The WIP branch is located
>> at: <https://github.com/jdufresne/django/tree/date-register-lookup>
>>
>> Would this be something welcome as a ticket and pull request? While
>> there is no outward change in functionality, I see it as a beneficial
>> refactoring because with this change:
>>
>> 1. The year, month, day, etc lookups are no longer treated as special
>> cases, but instead use the common code path.
>> 2. There now exists complete and useful examples of registering new
>> lookups in the Django code itself. This might help others build more
>> lookups.
>> 3. The lookups are now limited to the correct Field types where as
>> previously this was not true. I demonstrate this with a unit test.
>>
>> If this looks like it could be a welcome change I will can go forward
>> with a typical ticket and pull request.
>>
>> Cheers,
>> Jon
>>
>> [0] https://docs.djangoproject.com/en/dev/howto/custom-lookups/
>> [1] https://docs.djangoproject.com/en/dev/ref/models/querysets/#year
>>
>
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