Question

I’m just getting my hands on Django Managers and I’ve found myself doing this type of programming. I’m looking to see if there is a way to remove the obvious repetition.. I believe I need to define use get_query_set to refer to myself?

To be very clear on my question. I am repeatadly having to pass in the subdivision in order to figure out the rows from which to filter on. I think there is an easier way I’m just not sure what it is.

Thanks for looking!!

— models.py

class Subdivision(models.Model):
    objects = SubdivisionManager()

— managers.py

class SubdivisionManager(models.Manager):
    """A generic manager with metros"""


    def is_metro_sample_eligible(self, subdivision_id):
        """Are we eligible for sampling taking into account the 90 day windows"""
        from .models import Subdivision
        subdivision = Subdivision.objects.get(id=subdivision_id)
        return True


    def get_available_subdivisions(self, subdivision_id):
        """Return all potential subdivisions for a builder in a metro"""
        from .models import Subdivision
        subdivision = Subdivision.objects.get(id=subdivision_id)
        return self.filter(builder_org=subdivision.builder_org,
                           metro=subdivision.metro)

    def get_available_sampling_subdivisions(self, subdivision_id):
        """Return Subdivision which are able to participate in metro sampling"""
        from .models import Subdivision
        subdivision = Subdivision.objects.get(id=subdivision_id)
        return self.filter(builder_org=subdivision.builder_org,
                           metro=subdivision.metro,
                           use_sampling = True,
                           use_metro_sampling = True)

Answer 1

Actually, I’d put is_metro_sample_eligible() on Subdivision, since each call needs to access an instance.

class Subdivision(models.Model):
    def is_metro_sample_eligible(self):
        """Are we eligible for sampling taking into account the 90 day windows"""
        #TODO do something useful here and return true or false
        return True

And then I’d either move get_available_subdivisions() and get_available_sampling_subdivisions() onto your builder_org model

from .models import Subdivision

class BuilderOrg(models.Model):
    #whatever you have goes here
    def get_available_subdivisions(self, metro):
        """Return all potential subdivisions for a builder in a metro"""
        return Subdivision.objects.filter(builder_org=self,
                                          metro=metro)

    def get_available_sampling_subdivisions(self, metro):
        """Return Subdivision which are able to participate in metro sampling"""
        return Subdivision.objects.filter(builder_org=self,
                                          metro=metro,
                                          use_sampling = True,
                                          use_metro_sampling = True)

or leave it on the manager, and revise the signature to get_available_subdivisions(self, builder_org, metro).

Rationale- I could imagine needing to call get_available_subdivisions() without actually having a Subdivision already in mind- clearly the important pieces of information are the builder organization and the metro.