id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
24042	Custom AutoField fields do not work correctly on postgres	Lucas Wiman	nobody	"Patch also available at https://github.com/django/django/pull/3776

The  documentation (https://docs.djangoproject.com/en/dev/howto/custom-model-fields/#emulating-built-in-field-types) on Field.get_internal_type implies that it should define custom behavior and ensure that database-correct behavior is followed. For Postgres (though not for sqlite), specifying get_internal_type() to be ""AutoField"" fails to correctly set the field, leading to errors like this:

{{{
test_auto_field (field_subclassing.tests.CustomField) ... ERROR

======================================================================
ERROR: test_auto_field (field_subclassing.tests.CustomField)
----------------------------------------------------------------------
Traceback (most recent call last):
  File ""/Users/lucaswiman/opensource/django/tests/field_subclassing/tests.py"", line 128, in test_auto_field
    o.save()
  File ""/Users/lucaswiman/opensource/django/django/db/models/base.py"", line 694, in save
    force_update=force_update, update_fields=update_fields)
  File ""/Users/lucaswiman/opensource/django/django/db/models/base.py"", line 722, in save_base
    updated = self._save_table(raw, cls, force_insert, force_update, using, update_fields)
  File ""/Users/lucaswiman/opensource/django/django/db/models/base.py"", line 803, in _save_table
    result = self._do_insert(cls._base_manager, using, fields, update_pk, raw)
  File ""/Users/lucaswiman/opensource/django/django/db/models/base.py"", line 842, in _do_insert
    using=using, raw=raw)
  File ""/Users/lucaswiman/opensource/django/django/db/models/manager.py"", line 131, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File ""/Users/lucaswiman/opensource/django/django/db/models/query.py"", line 954, in _insert
    return query.get_compiler(using=using).execute_sql(return_id)
  File ""/Users/lucaswiman/opensource/django/django/db/models/sql/compiler.py"", line 931, in execute_sql
    cursor.execute(sql, params)
  File ""/Users/lucaswiman/opensource/django/django/db/backends/utils.py"", line 65, in execute
    return self.cursor.execute(sql, params)
  File ""/Users/lucaswiman/opensource/django/django/db/utils.py"", line 95, in __exit__
    six.reraise(dj_exc_type, dj_exc_value, traceback)
  File ""/Users/lucaswiman/opensource/django/django/db/backends/utils.py"", line 65, in execute
    return self.cursor.execute(sql, params)
IntegrityError: null value in column ""id"" violates not-null constraint
DETAIL:  Failing row contains (null).
}}}

The attached diff adds a regression test which fails on postgres databases with the error above. I also fixed all other uses of isinstance(..., AutoField) I could find in the code. 

The immediate motivation for this is writing integration tests which use django-salesforce on a CI system that uses a postgres database. I've filed a separate issue there, though I think fixing the behavior in Django to match the documentation would be a preferable solution. The package maintainer for django-salesforce agrees (https://github.com/django-salesforce/django-salesforce/issues/90#issuecomment-67932443).

'''How to Reproduce'''

Check out the master branch and apply my diff from the tests/ directory. Run the tests with a settings file pointing to a postgres database:
{{{
PYTHONPATH=..:$PYTHONPATH ./runtests.py --verbosity=2 --failfast field_subclassing --settings=test_postgres
}}}
It will fail with the above stack trace.

'''Testing'''

I verified that the regression test fails without the remainder of the diff. I also verified that the tests still pass on the default test_sqlite file."	Uncategorized	new	Uncategorized	dev	Normal				Unreviewed	1	0	0	0	0	0