How to query abstract-class-based objects in Django?

user_422073 0
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Let's say I have an abstract base class that looks like this:

class StellarObject(BaseModel):
  title = models.CharField(max_length=255)
  description = models.TextField()
  slug = models.SlugField(blank=True, null=True)

  class Meta:
    abstract = True

Now, let's say I have two actual database classes that inherit from StellarObject

class Planet(StellarObject):
  type = models.CharField(max_length=50)
  size = models.IntegerField(max_length=10)

class Star(StellarObject):
  mass = models.IntegerField(max_length=10)

So far, so good. If I want to get Planets or Stars, all I do is this:

Thing.objects.all() #or
Thing.objects.filter() #or count(), etc...

But what if I want to get ALL StellarObjects? If I do:

StellarObject.objects.all()

It of course returns an error, because an abstract class isn't an actual database object, and therefore cannot be queried. Everything I've read says I need to do two queries, one each on Planets and Stars, and then merge them. That seems horribly inefficient. Is that the only way?

abstract-class django
7 Answers

You can't query abstract base classes. For multi-table inheritance you can use django-model-utils and it's InheritanceManager, which extends standard QuerySet with select_subclasses() method, which does right that you need: it left-joins all inherited tables and returns appropriate type instance for each row.

user_8181160
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