Cannot resolve operation dependencies

[Gabe Jackson]

The auto detector cannot create migrations for the project located at: ​https://github.com/gabejackson/django-migration-test
Using Django==1.7c2 and python 2.7.5
The command used is:

./manage.py makemigrations --dry-run

which leads to:

Traceback (most recent call last):
  File "./manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/Users/gabejackson/venv/django-1.7/lib/python2.7/site-packages/django/core/management/__init__.py", line 385, in execute_from_command_line
    utility.execute()
  File "/Users/gabejackson/venv/django-1.7/lib/python2.7/site-packages/django/core/management/__init__.py", line 377, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/Users/gabejackson/venv/django-1.7/lib/python2.7/site-packages/django/core/management/base.py", line 288, in run_from_argv
    self.execute(*args, **options.__dict__)
  File "/Users/gabejackson/venv/django-1.7/lib/python2.7/site-packages/django/core/management/base.py", line 337, in execute
    output = self.handle(*args, **options)
  File "/Users/gabejackson/venv/django-1.7/lib/python2.7/site-packages/django/core/management/commands/makemigrations.py", line 111, in handle
    convert_apps=app_labels or None,
  File "/Users/gabejackson/venv/django-1.7/lib/python2.7/site-packages/django/db/migrations/autodetector.py", line 50, in changes
    changes = self._detect_changes(convert_apps, graph)
  File "/Users/gabejackson/venv/django-1.7/lib/python2.7/site-packages/django/db/migrations/autodetector.py", line 288, in _detect_changes
    raise ValueError("Cannot resolve operation dependencies")
ValueError: Cannot resolve operation dependencies

[Gabe Jackson]

I further reduced the model to only 2 apps and 4 models. I found out that the auto-detector is non-deterministic depending on the alphabetical names of the models.
If you run the project with the class APackage it will fail with "Cannot resolve operation deps". If you rename APackage to DPackage (DPackage is alphabetically now later than DeliveryCountry) and run makemigrations --dry-run again, it works...

Apparently there is some issue with sorting classes alphabetically. Hope this helps..

[Collin Anderson]

I get the same error with these simple models on the latest code. It's a circular dependency of ForeignKeys between apps, and I don't see anything saying that this isn't supported.

[Collin Anderson]

I've reproduced the project from scratch just to be sure. Here are the simple models: ​https://github.com/collinanderson/ticket23315/commit/39c36c953e96a9eede4f77e161ee3bf96a3ded7b

[Andrew Godwin <andrew@…>]

In 9247da1032c1b8c98b0fcfb278bbbdbc8edc8783:

Fixed #23315: Operational dependency fail with mixed create/add

[Andrew Godwin <andrew@…>]

In 824e02bf836affa182dd4bcb7b3e1796f1389b38:

[1.7.x] Fixed #23315: Operational dependency fail with mixed create/add

[Tim Graham]

The new test fails on Python 3.4:

======================================================================
ERROR [0.001s]: test_circular_dependency_mixed_addcreate (migrations.test_autodetector.AutodetectorTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/jenkins/workspace/django-master/database/sqlite3/python/python3.4/tests/migrations/test_autodetector.py", line 1099, in test_circular_dependency_mixed_addcreate
    changes = autodetector._detect_changes()
  File "/home/jenkins/workspace/django-master/database/sqlite3/python/python3.4/django/db/migrations/autodetector.py", line 172, in _detect_changes
    self.generate_created_models()
  File "/home/jenkins/workspace/django-master/database/sqlite3/python/python3.4/django/db/migrations/autodetector.py", line 497, in generate_created_models
    dep_app_label = field.rel.to._meta.app_label
AttributeError: 'str' object has no attribute '_meta'

The string is "a.person" (but resolves to <class 'Person'> when the test passes).

[Tim Graham]

I'm looking into this. It seems to be a non-deterministic issue, perhaps ordering related.

[Andrew Godwin]

That's odd, because all the other relationships in that test file are fine under 3.4. It's likely an issue in the State's reconstruction of it. Happy to look at this instead if you want to hand it over.

[Tim Graham <timograham@…>]

In d1299fce0eeeb2a7749fecafc87260462e75aac9:

Fixed migrations tests added in refs #23315.

[Tim Graham <timograham@…>]

In 6981eced83ea2d6462b21c12ecea044e02e56d05:

[1.7.x] Fixed migrations tests added in refs #23315.

Backport of d1299fce0e from master

[Tim Graham]

do_pending_lookups wasn't resolving the field due to a case mismatch.

[Andrew Godwin <andrew@…>]

In 9247da1032c1b8c98b0fcfb278bbbdbc8edc8783:

Fixed #23315: Operational dependency fail with mixed create/add