From django 1.6 to 1.11: AppRegistryNotReady exception

Question

In my REST-like API, I have a mechanism to allow users to customize models (add custom fields and add custom models).

This relies on a set of models describing the customizations.

Here is a simplified version of my code to show the concept.

+ myproject
   + customization
      . models.py

class CustomModel(django.db.models.Model):
    # […]

class CustomField(django.db.models.Model):
    # […]

and

+ myproject
    + entities
        . models.py

class RootEntityModel(django.db.models.Model):
    name = CharField(…)
    # […]

from myproject import customization
from myproject.customization.models import CustomField 

# Here apply the custom filters on the root entity type
for custom_field in CustomField.objects.filter(entity__name='RootEntityModel').all():
    customize.build_field_and_apply(custom_field, RootEntityModel)

# Here instantiate custom models, etc
# […]

In Django 1.6, I have no problem making everything work.

Now, transitionning to Django 1.11, I've had some cleanup to do, mainly because it's impossible to import a model inside the root package of an application. (see also this answer).

I've eleminated every AppRegistryNotReady exception that I had, but for the one in myproject.entity.models module. Indeed, to build my Entities, I have to query to the CustomField and CustomModel tables, but as I'm currently building my models, Django forbids me to do so.

I am stuck in this kind of circular dependency. Any thought towards a workaround are welcome.

EDIT: Stack trace follows

  […]
  File "D:/Code/django-1.11/django/__init__.py", line 27, in setup
    apps.populate(settings.INSTALLED_APPS)
  File "D:/Code/django-1.11/django/apps/registry.py", line 108, in populate
    app_config.import_models()
  File "D:/Code/django-1.11/django/apps/config.py", line 202, in import_models
    self.models_module = import_module(models_module_name)
  File "C:/Python27/lib/importlib/__init__.py", line 37, in import_module
    __import__(name)
  File "D:/Code/resterserver/myproject/entities/models/__init__.py", line 369, in <module>
    for custom_field in CustomField.objects.filter(entity__name='RootEntityModel').all():
  File "D:/Code/django-1.11/django/db/models/manager.py", line 85, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "D:/Code/django-1.11/django/db/models/query.py", line 784, in filter
    return self._filter_or_exclude(False, *args, **kwargs)
  File "D:/Code/django-1.11/django/db/models/query.py", line 802, in _filter_or_exclude
    clone.query.add_q(Q(*args, **kwargs))
  File "D:/Code/django-1.11/django/db/models/sql/query.py", line 1250, in add_q
    clause, _ = self._add_q(q_object, self.used_aliases)
  File "D:/Code/django-1.11/django/db/models/sql/query.py", line 1276, in _add_q
    allow_joins=allow_joins, split_subq=split_subq,
  File "D:/Code/django-1.11/django/db/models/sql/query.py", line 1154, in build_filter
    lookups, parts, reffed_expression = self.solve_lookup_type(arg)
  File "D:/Code/django-1.11/django/db/models/sql/query.py", line 1034, in solve_lookup_type
    _, field, _, lookup_parts = self.names_to_path(lookup_splitted, self.get_meta())
  File "D:/Code/django-1.11/django/db/models/sql/query.py", line 1331, in names_to_path
    if field.is_relation and not field.related_model:
  File "D:/Code/django-1.11/django/utils/functional.py", line 35, in __get__
    res = instance.__dict__[self.name] = self.func(instance)
  File "D:/Code/django-1.11/django/db/models/fields/related.py", line 115, in related_model
    apps.check_models_ready()
  File "D:/Code/django-1.11/django/apps/registry.py", line 132, in check_models_ready
    raise AppRegistryNotReady("Models aren't loaded yet.")
django.core.exceptions.AppRegistryNotReady: Models aren't loaded yet.

Indeed, @anjaneyulu-batta, I've forgotten to join it. It's done. — Olivier H, Apr 25 '18 at 12:19
Apparently there's a `ready` hook in the new AppConfig class, that I can subclass for my own apps. I'll look into this and share my solution if it works. — Olivier H, Apr 27 '18 at 08:47

score 0 · Accepted Answer · answered Nov 22 '18 at 12:38

Instead of adding custom models directly in my models.py module, I do it instead in an AppConfig object by overriding its ready() method.

Here's the working code stub:

+ myproject
    + entities
        . apps.py

from django.apps.config import AppConfig

class EntitiesAppConfig(AppConfig):
    name = 'myproject.entities'
    label = 'entities'
    verbose_name = 'MyProject Entities app'
    def ready(self):
        super(EntitiesAppConfig, self).ready()

        # HERE i can do my customizations
        # ...

From django 1.6 to 1.11: AppRegistryNotReady exception

1 Answers1