Object creation assigns proxy class based on base model field(s)

user_4905992 0
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I'm hoping to be able to create an object using a base model but have that object actually be created as a proxy class depending on the object's field(s).

So for example, for the following models:

class Animal(models.Model):
    species = models.CharField()

class Cat(Animal):
    class Meta:
        proxy = True

class Dog(Animal):
    class Meta:
        proxy = True

How can I set it up so that

cat = Animal.objects.create(species="cat")
dog = Animal.objects.create(species="dog")

Animal.objects.all() # Returns queryset of [cat, dog]
Cat.objects.all() # Returns queryset of [cat]
Dog.objects.all() # Returns queryset of [dog]

Edit: I would be interested in both types of solutions:

a) The object is created as a Animal first then converted to the proxy class afterwards

b) The object is created directly as the proxy class

(Solution type A is probably most relevant to my use case unfortunately)

django-managers django-queryset django-models django
2 Answers

You should create a custom manager for each proxy.

class Animal(models.Model):
    species = models.CharField()

class CatManager(models.Manager):
    def get_queryset(self):
        return super().get_queryset().filter(species='cat')

class DogManager(models.Manager):
    def get_queryset(self):
        return super().get_queryset().filter(species='dog')

class Cat(Animal):
    objects = CatManager()
    class Meta:
        proxy = True

class Dog(Animal):
    objects = DogManager()
    class Meta:
        proxy = True
user_73959110

Define a custom manager for Animal which will filter the queryset based on the species. Here, we will use the class name as the basis of the species' name.

class AnimalManager(models.Manager):
    def get_queryset(self):
        if self.model is Animal:
            return super().get_queryset()
        return super().get_queryset().filter(species=self.model.__name__.casefold())

class Animal(models.Model):
    objects = AnimalManager()
    species = models.CharField(max_length=100)

class Cat(Animal):
    class Meta:
        proxy = True

class Dog(Animal):
    class Meta:
        proxy = True

Output

>>> from my_app.models import *
>>>
>>> # Create the animals
>>> Animal.objects.create(species="cat")
<Animal: Animal object (1)>
>>> Animal.objects.create(species="dog")
<Animal: Animal object (2)>
>>> Animal.objects.create(species="cat")
<Animal: Animal object (3)>
>>> Animal.objects.create(species="cat")
<Animal: Animal object (4)>
>>> Animal.objects.create(species="dog")
<Animal: Animal object (5)>
>>>
>>> # Query the animals
>>> Animal.objects.all()
<QuerySet [<Animal: Animal object (1)>, <Animal: Animal object (2)>, <Animal: Animal object (3)>, <Animal: Animal object (4)>, <Animal: Animal object (5)>]>
>>> Cat.objects.all()
<QuerySet [<Cat: Cat object (1)>, <Cat: Cat object (3)>, <Cat: Cat object (4)>]>
>>> Dog.objects.all()
<QuerySet [<Dog: Dog object (2)>, <Dog: Dog object (5)>]>
user_110438250
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