Sure - but you can always save the expression to a variable and use it 
multiple times.

mycalc = MyFunc('a', 'b')
Model.objects.filter(GreaterEqual(mycalc, 0.6)).order_by(mycalc)

I think we already have the building blocks we need to avoid adding another 
queryset method.

On Saturday, 10 March 2018 14:01:41 UTC+11, Cristiano Coelho wrote:
>
> It wouldn't work if you also want to order by the annotated value.
>
> El viernes, 9 de marzo de 2018, 8:27:36 (UTC-3), Josh Smeaton escribió:
>>
>> Would teaching filter() and friends to use expressions directly solve 
>> your issue? You suggested using `alias` upthread, but that's only really 
>> required so you can refer to it later? Unless you wanted to refer to the 
>> field more than once, having each queryset method respect expressions 
>> should be enough I think.
>>
>> https://github.com/django/django/pull/8119 adds boolean expression 
>> support to filter. I believe most other queryset methods have support for 
>> expressions now (order_by, values/values_list).
>>
>> For the alias used multiple times case, it should be enough to annotate 
>> and then restrict with values if you don't actually want it in the 
>> select/group list.
>>
>> On Friday, 9 March 2018 00:22:00 UTC+11, Cristiano Coelho wrote:
>>>
>>> The workaround, although extremely ugly and which will probably cause 
>>> issues in the future (reason I only used it for the model I needed to do 
>>> those odd queries) was to use a custom queryset/manager. Something like 
>>> this.
>>>
>>> class FasterCountQuerySet(QuerySet):
>>>     def count(self):
>>>         return super(FasterCountQuerySet, self.values('pk')).count()
>>> FasterCountManager = Manager.from_queryset(FasterCountQuerySet)
>>>
>>> But again, this is extremely ugly and will still cause a subquery, but 
>>> without the unnecessary group by and extra function calls.
>>>
>>>
>>> El miércoles, 7 de marzo de 2018, 19:48:01 (UTC-3), Jared Proffitt 
>>> escribió:
>>>>
>>>> I have also run into this exact problem. Would love to get this fixed. 
>>>> Have you found a good workaround?
>>>>
>>>> On Tuesday, December 26, 2017 at 12:37:16 PM UTC-6, Cristiano Coelho 
>>>> wrote:
>>>>>
>>>>> Hello, I'm having a hard time explaining the exact issue but I hope 
>>>>> it's clear enough.
>>>>>
>>>>>
>>>>> Following this issue (
>>>>> https://groups.google.com/forum/#!searchin/django-users/cristiano%7Csort:date/django-users/q6XdfyK29HA/TcE8oFitBQAJ)
>>>>>  
>>>>> from django users and a related ticket (
>>>>> https://code.djangoproject.com/ticket/27719) that seems to be left 
>>>>> out or forgotten already.
>>>>>
>>>>> There has to be a way to alias or annotate a value given an expression 
>>>>> or SQL Function that doesn't necessarily aggregates data but rather work 
>>>>> on 
>>>>> a single value.
>>>>>
>>>>> Right now as shown on the django-users post, using annotate for this 
>>>>> purpose will cause unexpected grouping and sub querying that could result 
>>>>> in very slow and hard to debug queries.
>>>>>
>>>>> The core issue is that using annotate without a previous call either 
>>>>> vaues or values_list, will work as expected, simply annotating a value 
>>>>> and 
>>>>> returning it as an additional column, but if an aggregate is added 
>>>>> afterwards (such as count), the final query ends up being a redundant 
>>>>> query 
>>>>> where the annotated value is added to a group by clause (group by id + 
>>>>> column), to a column as part of the select (function called twice) and 
>>>>> then 
>>>>> wrapped into a select * (subquery), which makes the extra column as part 
>>>>> of 
>>>>> the select and group by useless, unless the query had any kind of 
>>>>> left/inner join in which case the group by might make sense (although not 
>>>>> sure about the column showing up on the select clause)
>>>>>
>>>>> The ugly work around is to simply add a .values('id') at the end so 
>>>>> the annotated value doesn't show on the group by and select sections, 
>>>>> although the nested query still happens.
>>>>>
>>>>>
>>>>> For this reason, there's currently no way to achieve the above without 
>>>>> ugly work arounds or unnecessary database performance hits.
>>>>>
>>>>> The easiest option I believe would be to follow the ticket in order to 
>>>>> implement an alias call that works exactly like annotate but doesn't 
>>>>> trigger any grouping.
>>>>>
>>>>> A more complicated option is probably trying to make 
>>>>> annotate/aggregate smarter, so all the unnecessary grouping and sub 
>>>>> querying doesn't happen unless needed, for example, if the queryset 
>>>>> didn't 
>>>>> call values/values_list or if there are no relationships/joins used.
>>>>>
>>>>>
>>>>> Example/demostration:
>>>>>
>>>>> Given the following queryset
>>>>>
>>>>> query1 = MyModel.objects.annotate(x=MyFunction('a', 'b')).filter(
>>>>> x__gte=0.6).order_by('-x')
>>>>>
>>>>>
>>>>> query1 SQL is good and looks like:
>>>>>
>>>>> SELECT id, a, b, myfunction(a, b) as x
>>>>> FROM mymodel
>>>>> WHERE myfunction(a, b) >= 0.6
>>>>> ORDER BY x desc
>>>>>
>>>>> Notice how there's no group by, the ORM was smart enough to not 
>>>>> include it since there was no previous call to values/values_list
>>>>>
>>>>>
>>>>> If we run query1.count() the final SQL looks like:
>>>>>
>>>>> SELECT COUNT(*) FROM (
>>>>>     SELECT id, myfunction(a, b) as x
>>>>>     FROM mymodel
>>>>>     WHERE myfunction(a ,b) >= 0.6
>>>>>     GROUP BY id, myfunction(a ,b)
>>>>> ) subquery
>>>>>
>>>>> which if myfunction is slow, will add a massive slow down that's not 
>>>>> even needed, and should actually be just:
>>>>>
>>>>> SELECT count(*)
>>>>> FROM mymodel
>>>>> WHERE myfunction(a ,b) >= 0.6
>>>>>
>>>>>
>>>>> while the other query should ONLY happen if the group by makes sense 
>>>>> (i.e, if there's a join somewhere, or a values/values_list was used 
>>>>> previously so id is not part of the group by statement)
>>>>>
>>>>> but if we work around the issue adding a query1.values('id').count(), 
>>>>> the final query ends up better:
>>>>>
>>>>> SELECT COUNT(*) FROM (
>>>>>     SELECT id
>>>>>     FROM mymodel
>>>>>     WHERE myfunction(a ,b) >= 0.6
>>>>> ) subquery
>>>>>
>>>>>
>>>>> I hope I could explain this clear enough with the example, and note 
>>>>> that using a custom lookup is not possible since the value is required 
>>>>> for 
>>>>> the order_by to work.
>>>>>
>>>>>
>>>>>

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