#16647: Default filters: pacth to add QuerySet support for random plus a new
shuffle filter
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Reporter: h3 | Owner: nobody
Type: New | Status: new
feature | Component: Template system
Milestone: | Severity: Normal
Version: 1.3 | Keywords:
Resolution: | Has patch: 1
Triage Stage: Design | Needs tests: 1
decision needed | Easy pickings: 0
Needs documentation: 1 |
Patch needs improvement: 1 |
UI/UX: 0 |
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Comment (by h3):
> If the queryset has already been evaluated, you could just transform it
to a list and perform the ordinary random/shuffle operations on that, I
suppose... would that be faster?
I will have to make some tests to tell
> I am not sure this is a good idea. The problem is that
qs.order_by('?')[0] might be really expensive. If I am not mistaken, the
DB must go through the whole result set and sort everything. Even if the
DB returns just one row, that can be expensive. I am afraid that users of
random do not realize this, as how could a fetch of just a single object
cost much...
>
> Also, in the patch you use len(qs). That means the queryset gets
evaluated (or at least count(*) is evaluated) there. try - except
indexerror is better.
This strengthen my feeling that these functionality (random/shuffle filter
for qs) should really be included by django core.
What I did was the "obvious" way of doing it and it's how a lot of django
developers will implement it the day they'll need this functionality.
Now the question is, what's the optimal way to do it..
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Ticket URL: <https://code.djangoproject.com/ticket/16647#comment:4>
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