I've seen *extra()* misused in cases where developers came from a
background of writing raw SQL and then used it rather than figuring out the
(often relatively simple) ORM way of doing it. This is then a big
maintenance burden, and the harsher warning against its use is a good idea.
Also thanks for documenting *RawSQL*, didn't realize it was usable until
now so I've been able to get rid of some *extra()* usage in django-mysql.
On Wednesday, August 5, 2015 at 1:09:30 AM UTC+1, Josh Smeaton wrote:
>
> You're right about that. You can aggregate over custom expressions. For
> aggregating over enums you should be able to use case expressions
>
> On Wed, 5 Aug 2015 at 05:05 Anssi Kääriäinen <akaa...@gmail.com
> <javascript:>> wrote:
>
>> On Tuesday, August 4, 2015, Shai Berger <sh...@platonix.com <javascript:>>
>> wrote:
>>>
>>> The classic database aggregation examples involve aggregation over time:
>>> Sum
>>> of sales per quarter (which is, itself, a function over date); average
>>> temparature per month; etc. All these require group-by clauses which name
>>> (expressions over) columns which are not FKs.
>>>
>>>
>> The following should work:
>>
>>
>>
>> qs.annotate(quarter=Quarter('sold_date')).values('quarter').annotate(sum=Sum('amount'))
>>
>> I recall some changes to how the group by expression is generated for
>> expressions. If I recall correctly the group by should have the expression
>> itself now, not the base columns of the expression.
>>
>> There are many similar examples involving "enum columns" -- columns with a
>>> limited set of choices, where the choices are not instances of another
>>> model.
>>
>>
>> I'm not sure of this one.
>>
>> - Anssi
>>
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