Opened 4 years ago
Closed 3 years ago
#20930 closed New feature (duplicate)
Arithmetic operations on aggregates
Reported by: | Debanshu Kundu | Owned by: | |
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Component: | Database layer (models, ORM) | Version: | master |
Severity: | Normal | Keywords: | aggregate, annotate |
Cc: | Debanshu Kundu, jorgecarleitao@… | Triage Stage: | Accepted |
Has patch: | yes | Needs documentation: | yes |
Needs tests: | yes | Patch needs improvement: | yes |
Easy pickings: | no | UI/UX: | no |
Description
In many cases one may require to do simple arithmetic operations (+, -, *, /) on aggregated (with numbers or other aggregates).
Eg. For model Xyz
:
class Xyz(models.Model): a = models.IntegerField() b = models.IntegerField()
If I want to find percent ratio of sum of all a
and sum of all b
, I can write:
Xyz.objects.aggregate(ratio_percent=Sum('a')/Sum('b')*100)
This type of functionality has been implemented in this commit https://github.com/debanshuk/django/commit/722f7a4a17870fe1ffb6c207153d1fca6388a401
More operations (like pow) can also be added.
Change History (14)
comment:1 Changed 4 years ago by
comment:2 Changed 4 years ago by
Keywords: | aggregate annotate added |
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comment:3 follow-up: 4 Changed 4 years ago by
Hi debanshuk,
Wouldn't it be possible to make the same calculation outside of the aggregate? That seems cleaner to me.
Wim
comment:4 Changed 4 years ago by
Hi Wim,
In the example given in the description, it would. And I guess in case of aggregates it would always be possible to make the calculations out side aggregate.
But, in case of annotate it would not. Well, it would certainly be possible, but wouldn’t be cleaner, as one would have to do the calculations for each element in resultant query-set.
Eg. Let modified Xyz
be:
class Xyz(models.Model): user = models.ForeignKey(User) a = models.IntegerField() b = models.IntegerField()
Now if I want to find percent ratio of sum of all a
and sum of all b
of a user
, for each user
. I may write:
Xyz.objects.values('user').annotate(ratio_percent=Sum('a')/Sum('b')*100)
Currently, to do this (without writing raw SQL), one would have to do something like:
result = Xyz.objects.values('user').annotate(total_a=Sum('a'), total_b=Sum('b')) final_result = [{'user': r['user'], 'ratio_percent': r['total_a']/r['total_b']*100} for r in result]
Also, If someone want to aggregate over annotation results, like in the example if I want to find maximum of the percentages, I may do:
Xyz.objects.values('user').annotate(ratio_percent=Sum('a')/Sum('b')*100).aggregate(Max('ratio_percent'))
Currently, I would have to do:
result = Xyz.objects.values('user').annotate(total_a=Sum('a'), total_b=Sum('b')) final_result = max(r['total_a']/r['total_b']*100 for r in result)
In the second one, max calculation in done in python. In the first one it is done in SQL itself.
Debanshu Kundu.
comment:6 Changed 4 years ago by
Well...not exactly duplicate, as #14030 is for something like this:
Xyz.objects.aggregate(Sum(F('a')/F('b')*100))
but I guess #14030 can be extended to implement functionality of this ticket. In case of annotate
something like this can be done:
Xyz.objects.values('user').annotate(total_a=Sum('a'), total_b=Sum('b')).values('user', ratio_percent=F('total_a')/F('total_b')*100)
But, in case of aggregate
this wont work as aggregate
returns dict
(not QuerySet
). So, I guess some changes are required for aggregate
. Also, both functionalities (operations on aggregates and passing F objects to aggregates) can co-exist (as I think).
comment:7 Changed 4 years ago by
Needs documentation: | set |
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Needs tests: | set |
Patch needs improvement: | set |
Triage Stage: | Unreviewed → Accepted |
comment:8 Changed 4 years ago by
Owner: | changed from nobody to Debanshu Kundu |
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Status: | new → assigned |
comment:9 Changed 4 years ago by
Added pull request https://github.com/django/django/pull/1510. Fixed code and added tests and docs.
comment:10 Changed 4 years ago by
Did amendment in the commit. Updated some conditions in test-cases to make them more reliable.
comment:11 Changed 4 years ago by
Owner: | Debanshu Kundu deleted |
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Status: | assigned → new |
comment:12 Changed 3 years ago by
Cc: | jorgecarleitao@… added |
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comment:14 Changed 3 years ago by
Resolution: | → duplicate |
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Status: | new → closed |
Also added pull request https://github.com/django/django/pull/1484