Reverse access model through a “double” ForeignKey

[Gergely Polonkai]

Hello,

I have three models:

• Build

• BuildGrouping, with a ForeignKey “build” pointing to Build

• Value, with a ForeignKey “grouping” that points to BuildGrouping

Right now, I also have Value.build, which is a ForeignKey to Build, so I can access the list of Values directly from a Build.

This setup, though, doesn’t feel right, as it contains redundancy. Is there a way to access the list of Values directly from Build without having this redundancy?

Thank you in advance!

Best,

Gergely

[Carsten Fuchs]

Am 14.10.2015 um 11:11 schrieb Gergely Polonkai:
> This setup, though, doesn’t feel right, as it contains redundancy. Is there a way to
> access the list of Values directly from Build without having this redundancy?

Well, you can filter your Value queryset by Build, see
https://docs.djangoproject.com/en/1.8/topics/db/queries/#lookups-that-span-relationships

Or, starting with a Build instance, you can work towards the Value instances, see
https://docs.djangoproject.com/en/1.8/topics/db/queries/#related-objects

Best regards,
Carsten

[Vijay Khemlani]

Value.objects.filter(grouping__build=your_build) I guess

You can add it as a method to the Build class

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[Gergely Polonkai]

Hello,

I just solved it, and went with a @property. On Build I have:

@property

def values(self):

    return Value.objects.filter(grouping__build=self)

and on the Value I have:

@property

def build(self):

    return self.grouping.build

This way I stay backwards compatible and didn’t even have to change my templates and such. Thanks for the tips, though!

Best,

Gergely

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