Unable to unpickle models from an external script

[Claude Paroz]

I'm using Python rq stack to delegate some tasks from my Django app to a queued system. In some of those tasks, models are pickled and then unpickled by rq. Unfortunately, with Django 1.7, I'm getting AppRegistryNotReady errors:

Traceback (most recent call last):
  File "/usr/local/bin/rqworker", line 9, in <module>
    load_entry_point('rq==0.4.6', 'console_scripts', 'rqworker')()
  File "/usr/local/lib/python2.7/dist-packages/rq/scripts/rqworker.py", line 100, in main
    w.work(burst=args.burst)
  File "/usr/local/lib/python2.7/dist-packages/rq/worker.py", line 358, in work
    self.execute_job(job)
  File "/usr/local/lib/python2.7/dist-packages/rq/worker.py", line 422, in execute_job
    self.main_work_horse(job)
  File "/usr/local/lib/python2.7/dist-packages/rq/worker.py", line 457, in main_work_horse
    success = self.perform_job(job)
  File "/usr/local/lib/python2.7/dist-packages/rq/worker.py", line 473, in perform_job
    job.func_name,
  File "/usr/local/lib/python2.7/dist-packages/rq/job.py", line 226, in func_name
    self._unpickle_data()
  File "/usr/local/lib/python2.7/dist-packages/rq/job.py", line 194, in _unpickle_data
    self._func_name, self._instance, self._args, self._kwargs = unpickle(self.data)
  File "/usr/local/lib/python2.7/dist-packages/rq/job.py", line 48, in unpickle
    obj = loads(pickled_string)
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/base.py", line 1464, in model_unpickle
    model = apps.get_model(*model_id)
  File "/usr/local/lib/python2.7/dist-packages/django/apps/registry.py", line 199, in get_model
    self.check_models_ready()
  File "/usr/local/lib/python2.7/dist-packages/django/apps/registry.py", line 131, in check_models_ready
    raise AppRegistryNotReady("Models aren't loaded yet.")
django.core.exceptions.AppRegistryNotReady: (AppRegistryNotReady("Models aren't loaded yet.",), <function model_unpickle

As you can see in the stack trace, my code has no chance to fix this as it is not called before the unpickling process.

One idea could be to check the app registry state in model_unpickle and populate it if needed. Thoughts?

[Claude Paroz]

​https://github.com/django/django/pull/3747

[Claude Paroz]

Oh, and I'd really like to backport this to 1.7 as it appears to be a regression.

[Claude Paroz <claude@…>]

In 108b8bf852c76855ed98f5abe55db1da845598e7:

Fixed #24007 -- Ensure apps registry's ready before unpickling models

This prevents AppRegistryNotReady errors when unpickling Django
models from an external script.

[Claude Paroz <claude@…>]

In 47912d9f2b8f55044aef5b8ed9b006e8dd8ce976:

[1.7.x] Fixed #24007 -- Ensure apps registry's ready before unpickling models

This prevents AppRegistryNotReady errors when unpickling Django
models from an external script.
Backport of 108b8bf85 from master.

[Collin Anderson]

Regression in the test.
​https://github.com/django/django/pull/3749

[Tim Graham <timograham@…>]

In 4fb38b73073dcd54f4af41a2af14dbc36f5d9f33:

Allowed Python executable names other than python in test from refs #24007.

[Tim Graham]

Another problem with the test when running it outside the tests directory:

$ ./tests/runtests.py model_regress
Testing against Django installed in '/home/tim/code/django/django'
Creating test database for alias 'default'...
Creating test database for alias 'other'...
.............s..Traceback (most recent call last):
  File "/home/tim/code/django/tmpCkJ7D2.py", line 9, in <module>
    article = pickle.loads(data)
  File "/usr/lib/python2.7/pickle.py", line 1382, in loads
    return Unpickler(file).load()
  File "/usr/lib/python2.7/pickle.py", line 858, in load
    dispatch[key](self)
  File "/usr/lib/python2.7/pickle.py", line 1133, in load_reduce
    value = func(*args)
  File "/home/tim/code/django/django/db/models/base.py", line 1662, in model_unpickle
    apps.populate(settings.INSTALLED_APPS)
  File "/home/tim/code/django/django/apps/registry.py", line 85, in populate
    app_config = AppConfig.create(entry)
  File "/home/tim/code/django/django/apps/config.py", line 87, in create
    module = import_module(entry)
  File "/usr/lib/python2.7/importlib/__init__.py", line 37, in import_module
    __import__(name)
ImportError: No module named model_regress
F.
======================================================================
FAIL: test_unpickling_when_appregistrynotready (model_regress.test_pickle.ModelPickleTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/tim/code/django/tests/model_regress/test_pickle.py", line 88, in test_unpickling_when_appregistrynotready
    self.fail("Unable to reload model pickled data")
AssertionError: Unable to reload model pickled data

----------------------------------------------------------------------

[Claude Paroz]

One solution: ​https://github.com/django/django/pull/3758, but I may miss some simpler resolution.

[Claude Paroz <claude@…>]

In 1d9fc5caa947ff4ee72180185e91a9a145171712:

Made model_regress unpickling test CWD-independent

Refs #24007. Thanks Tim Graham for his help with the patch.

[Tim Graham <timograham@…>]

In 995be4a1375340a53668dd80444756d77302000d:

Fixed refs #24007 test on Windows.

[Tim Graham <timograham@…>]

In ea1865223886295674422923a2a9d38bacb0564d:

[1.7.x] Made model_regress unpickling test CWD-independent

Refs #24007. Thanks Tim Graham for his help with the patch.

Backport of 1d9fc5caa947ff4ee72180185e91a9a145171712 and
995be4a1375340a53668dd80444756d77302000d from master

[Tim Graham <timograham@…>]

In 5338ff4808c822a8b00e90154b884b7be3011e60:

Fixed #24160 -- Fixed model_regress test on Windows; refs #24007.

[Tim Graham <timograham@…>]

In cef3f805c21c029d017e6704565f9f2f5746a1e5:

[1.7.x] Fixed #24160 -- Fixed model_regress test on Windows; refs #24007.

Backport of 5338ff4808c822a8b00e90154b884b7be3011e60 from master

[Tim Graham]

Reopening per ​discussion on django-dev which suggests this should be reverted.

​PR

[Tim Graham <timograham@…>]

In 10a16280:

Refs #24007 -- Removed an apps.populate() call in model unpickling that can cause deadlocks.