Comments on: Dynamic OR’d Queryset creation with Django

By: Dynamic OR’d Queryset Creation with Django « SRA Lab

Dynamic OR’d Queryset Creation with Django « SRA Lab — Thu, 27 Jan 2011 13:22:30 +0000

[...] complete posts and comments published on Elf Sternberg's blog, this is the method I found to create dynamic complex queryset with Django (Q and [...]

By: fayce

fayce — Sat, 07 Nov 2009 22:54:58 +0000

I found the solution ! and it works !!

I had to combine Travis Cline method and some dicts and everything works just fine…

So, if someone is interested to know more about how I did, feel free to ask.

By: fayce

fayce — Sat, 07 Nov 2009 19:41:11 +0000

Thank you for this post ! all thoses answers were helpful to me and really instructive... but I still can find how I can apply it to my problem even if it's really similar. Everything is dynamic in my queryset: - the logical operator ( | or &) - the operator (lte, gte, icontains ....) - the name of the field (what you call the mode?) - and the value... I would like to build the complete queryset from strings, like this: tab = [['field1','value1','operator1','logical-operator1'], ['field2','value2','operator2','logical-operator2'], ['field3','value3','operator3','logical-operator3'] ] for e in tab: req = req e[3] Q(e[0]__e[2]=e[1]) r = Obj.Objects.filter(req) I know this is completely wrong and will never work.. but this is the idea.. Thank you for you help !

By: Elf Sternberg

Elf Sternberg — Fri, 14 Aug 2009 16:49:38 +0000

Andre, yes, I know about the plural vs. singular. It’s correct in the production code; I slipped making the example. And as I pointed out to Brian, in the production code multiple remote applications are being sent requests for querysets that need to be OR’d for the final production. Would it work correctly for, say, “contains” as the argument? (There’s a lot of text string searching going on.)

By: Elf Sternberg

Elf Sternberg — Fri, 14 Aug 2009 16:47:42 +0000

Brian, that’s useful under most circumstances, but in actual usage, I was getting querysets generated from multiple, sometimes remote, sources, and needed them OR’d together for the final result. The snippet I posted was simply for illustrative purposes.

By: Brian Luft

Brian Luft — Fri, 14 Aug 2009 16:15:56 +0000

While OR’ing Q objects together can be useful in some scenarios (may not scale well), why didn’t you use something like:

Responses.objects.filter(mode__in=modes)

By: Andre LeBlanc

Andre LeBlanc — Fri, 14 Aug 2009 15:10:17 +0000

I’m about 90% sure that

qset = Responses.objects.filter(mode__in=modes)

would have the exact same effect.

also, naming a model after the plural form of the word is considered bad form. the model really should be called “Response” but thats just nitpicking.

By: Bartek

Bartek — Fri, 14 Aug 2009 14:14:08 +0000

To make it a list comprehension you can try something like this:

import operator

qset = reduce(operator.__or__, [Q(mode__exact=mode) for mode in modes[1:]])

Didn’t test it, but it should work. Perhaps it can even be improved

By: Ryan

Ryan — Fri, 14 Aug 2009 09:28:34 +0000

You could start off with qset = Q(), and then loop through all the modes, OR’ing them together, without having to check the length.

By: Travis Cline

Travis Cline — Fri, 14 Aug 2009 04:33:30 +0000

A slight golfing:

qset = Q()
for mode in modes:
qset |= Q(mode=mode)
r = Responses.objects.filter(qset)

or:

r = Responses.objects.filter(reduce(lambda x,y: x|Q(mode=y), modes, Q()))

But that’s probably getting too clever.