Abstract Django model manager

Question

I lack Python metaprogramming knowledge here. Let's say I have the following:

class OwnCompanyManager(models.Manager):
 """Only companies of this user"""
 def get_queryset(self, user):
 if user.is_superuser:
 return super(OwnCompanyManager, self).get_queryset()
 return super(OwnCompanyManager, self).get_queryset().filter(
 companyuser__user=user)
class OwnPublisherManager(models.Manager):
 """Only publishers of this user's company"""
 def get_queryset(self, user):
 if user.is_superuser:
 return super(OwnPublisherManager, self).get_queryset()
 return super(OwnPublisherManager, self).get_queryset().filter(
 company__companyuser__user=user)
class Company(models.Model):
 name = models.CharField(max_length=45)
 objects = models.Manager()
 own = OwnCompanyManager()
class Publisher(models.Model):
 company = models.ForeignKey(Company)
 allow_latest_dev = models.BooleanField(default=False)
 domains_blocked = models.BooleanField(default=False)
 objects = models.Manager()
 own = OwnPublisherManager()

I have many more than that. I dislike the copy-paste boilerplate Own(Publisher|Company|Etcetra)Manager). The only change is, as you can see, in the filter.

How can I abstract Own(InsertModelNameHere)Manager and use it from Company, Publisher and other models? I would like to specify the filter kwargs in manager definition.

Answer 1

There's no need for metaprogramming or anything particularly clever here. You just need to extract the bits that change. In this case, it's just the arguments to filter: you can use the dictionary form of argument passing, and store the filter as a string in a class attribute.

class AbstractManager(models.Manager):
 def get_queryset(self, user):
 if user.is_superuser:
 return super(AbstractManager, self).get_queryset()
 return super(AbstractManager, self).get_queryset().filter(**{self.filter: user})
class OwnCompanyManager(AbstractManager):
 filter = "companyuser__user"
class OwnPublisherManager(AbstractManager):
 filter = "company__companyuser__user"

• Motiejus Jakštys: This looks better. However, would it be possible to have AbstractManager and no other classes? I.e. construct the Manager class in the model definition?

Answer 2

Inspired by Daniel's reply:

class OwnManager(models.Manager):
 def __init__(self, key):
 super(OwnManager, self).__init__()
 self.k = key
 def get_queryset(self, user):
 if user.is_superuser:
 return super(OwnManager, self).get_queryset()
 return super(OwnManager, self).get_queryset().filter(**{self.k: user})
class Company(models.Model):
 name = models.CharField(max_length=45)
 objects = models.Manager()
 own = OwnManager("companyuser__user")
class Publisher(models.Model):
 company = models.ForeignKey(Company)
 allow_latest_dev = models.BooleanField(default=False)
 domains_blocked = models.BooleanField(default=False)
 objects = models.Manager()
 own = OwnManager("company__companyuser__user")

That way I don't want to create stupid class for every model.

Thanks Daniel.