Using Sum() for a models method inside a Query

[Jorge Andrés Vergara Ebratt]

Hello everyone,

Well, the tittle says it all:

I have a model X

class X(models.Model)

    a = models.IntegerField()

    b = models.IntegerField()

def getC(self):

    return a + b

So, when I'm inside a template I can call {{x.getC}} and it gets the method for the current instance it's in, but how can I get the Sum, or Avg of that method? I tried doing Sum('getC') but I get the error because getC isn't callable in the query...

Thanks in advance for the help

--

Jorge Andres Vergara Ebratt

#SoftwareDeveloper (Or at least trying to be)

@javebratt

facebook.com/javebratt

[Vijay Khemlani]

What do you mean by the sum or average of the method? As in the sum or average of the method applied to a list of objects "X"?

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[Ethan Blackburn]

related: https://groups.google.com/forum/#!topic/django-users/s9qgXC4TNrA

Short answer: you can't. A raw query would be your best bet(i.e. "SELECT SUM(a + b) AS sum FROM app_X")

[monoBOT]

You can create a model method (with no parameter) that can solve that, so you can call it from the templates.

something like:

class MyObject(models.Model):

    a = models.IntegerField()

    b = models.Integerfield()

    

    def miOperation(self):

        return self.a + self.b

    

    def miOtherOpertion(self):

        return self.a * self.b

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monoBOT

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[Jorge Andrés Vergara Ebratt]

Thanks, the best bet is the raw query, because I actually need the Sum of the method result for all the instances in the query...

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[monoBOT]

You can also do that using the ORM instead of SQL, just instead of doing the calls on the instanced model use a manager and do the calls on all the objects in the database, something like this:

class Objectmanager(models.Manager):

    def SumAB(self):

        return sum([(obj.a + obj.b) for obj in MyObject.objects.all()])

class MyObject(models.Model):

    a = models.IntegerField()

    b = models.Integerfield()

    objects = ObjectManager()

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