Finding object count where a field is unique in Django

Question

I have a model that is something like this:

class Input(models.Model):
        details = models.CharField(max_length=1000)
        user = models.ForeignKey(User)

class Case(Input):
    title  = models.CharField(max_length=200)
    views = models.IntegerField()

    class Argument(Input):
        case = models.ForeignKey(Case)
        side = models.BooleanField()

A user can submit many arguments, per case. I want to be able to say how many users have submitted side=true arguments.

I mean if 1 user had 10 arguments and another user had 2 arguments (both side=true) I'd want the count to be 2, not 12.

Update:

I am using these methods on the Case object:

 def users_agree(self):
        return self.argument_set.filter(side=True).values('user').distinct()
    def users_disagree(self):
        return self.argument_set.filter(side=False).values('user').distinct()

My template code calls count() on them.

I hope you are not actually using "case" Python keyword in your code. — Andriy Drozdyuk
– Andriy Drozdyuk, Commented May 26, 2009 at 18:58
I didn't know python has a keyword case. Can you refer me to docs on this? — Johnd
– Johnd, Commented May 26, 2009 at 19:40

Ayman Hourieh · Accepted Answer · 2009-05-10 18:29:23Z

9

Can you try:

Argument.objects.filter(side=True).values('case__user').distinct().count()

I think it does what you want. It issues one SQL query:

SELECT COUNT(DISTINCT "example_input"."user_id") FROM "example_argument" INNER JOIN "example_case" ON ("example_argument"."case_id" = "example_case"."input_ptr_id") INNER JOIN "example_input" ON ("example_case"."input_ptr_id" = "example_input"."id") WHERE "example_argument"."side" = True

Edit:

For this_case, get all users whose argument.side is True:

Argument.objects.filter(case__id=this_case.id, side=True).values('user').distinct()

edited May 10, 2009 at 18:29

answered May 10, 2009 at 18:13

Ayman Hourieh

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7 Comments

Johnd Over a year ago

Come to think of it, this should probably be done of the Case object. Like 'for this case show me how many users are on what side'

Ayman Hourieh Over a year ago

I've added another query to address your new requirement. Can you try?

Johnd Over a year ago

NameError: name 'this_case' is not defined

Ayman Hourieh Over a year ago

Yeah, you said "for this case show ...". Replace this_case with the Case object for which you want users whose argument.side is True.

Johnd Over a year ago

I'm gong to call this on a instance of a Case object, so I don't think I'll need to specify a case

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