Django Indexes with Model Inheritance

Question

I'm trying to add indexes for my abstract base class model so that its subclasses can also have the same index.

First I had this:

class Test(models.Model):
    id = models.BigAutoField(primary_key=True)
    class Meta:
        abstract = True
        indexes = models.Index(fields=['-id'])

class Testing1(Test):
    pass

class Testing2(Test):
    pass

Traceback:

  File "manage.py", line 21, in <module>
    main()
  File "manage.py", line 17, in main
    execute_from_command_line(sys.argv)
  File "C:\Users\yoom\Code\test\indexTestingVel\venv\lib\site-packages\django\core\management\__init__.py", line 381, in execute_from_command_line
    utility.execute()
  File "C:\Users\yoom\Code\test\indexTestingVel\venv\lib\site-packages\django\core\management\__init__.py", line 357, in execute
    django.setup()
  File "C:\Users\yoom\Code\test\indexTestingVel\venv\lib\site-packages\django\__init__.py", line 24, in setup
    apps.populate(settings.INSTALLED_APPS)
  File "C:\Users\yoom\Code\test\indexTestingVel\venv\lib\site-packages\django\apps\registry.py", line 114, in populate
    app_config.import_models()
  File "C:\Users\yoom\Code\test\indexTestingVel\venv\lib\site-packages\django\apps\config.py", line 211, in import_models
    self.models_module = import_module(models_module_name)
  File "C:\Users\yoom\Code\test\indexTestingVel\venv\lib\importlib\__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1006, in _gcd_import
  File "<frozen importlib._bootstrap>", line 983, in _find_and_load
  File "<frozen importlib._bootstrap>", line 967, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 677, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 728, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "C:\Users\yoom\Code\test\indexTestingVel\public\models.py", line 4, in <module>
    class Test(models.Model):
  File "C:\Users\yoom\Code\test\indexTestingVel\venv\lib\site-packages\django\db\models\base.py", line 305, in __new__
    new_class._meta.indexes = [copy.deepcopy(idx) for idx in new_class._meta.indexes]
TypeError: 'Index' object is not iterable

This is what I tried next only to get the EXACT same error:

class Test(models.Model):
    id = models.AutoField(primary_key=True)

    class Meta:
        abstract = True


class Testing1(Test):
    class Meta:
        indexes = models.Index(fields=['-id'])


class Testing2(Test):
    class Meta:
        indexes = models.Index(fields=['-id'])

Not sure what to do since I have more than just two subclasses and the abstract model has more than 20 columns.

Answer 1

The name indexes [Django-doc] is plural, it expects a list of Index objects [Django-doc]:

A list of indexes that you want to define on the model

So you should not assign an Index object itself, but a list of Index objects:

class Test(models.Model):
    id = models.BigAutoField(primary_key=True)
    class Meta:
        abstract = True
        indexes = [models.Index(fields=['-id'])]