Re: [Django] #28489: AttributeError: 'NoneType' object has no attribute 'is_relation' - None is undefined

[Django]

#28489: AttributeError: 'NoneType' object has no attribute 'is_relation' - None 
is
undefined
--+--
 Reporter:  Python Force  |Owner:  nobody
 Type:  Bug   |   Status:  closed
Component:  Migrations|  Version:  1.11
 Severity:  Normal|   Resolution:  duplicate
 Keywords:| Triage Stage:  Unreviewed
Has patch:  0 |  Needs documentation:  0
  Needs tests:  0 |  Patch needs improvement:  0
Easy pickings:  0 |UI/UX:  0
--+--
Changes (by Tim Graham):

 * status:  new => closed
 * resolution:   => duplicate


Comment:

 Looks like a duplicate of #28073. If you can provide steps to reproduce
 such as a sample project, please reopen that ticket.

-- 
Ticket URL: 
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[Django] #28489: AttributeError: 'NoneType' object has no attribute 'is_relation' - None is undefined

[Django]

#28489: AttributeError: 'NoneType' object has no attribute 'is_relation' - None 
is
undefined
+
   Reporter:  Python Force  |  Owner:  nobody
   Type:  Bug   | Status:  new
  Component:  Migrations|Version:  1.11
   Severity:  Normal|   Keywords:
   Triage Stage:  Unreviewed|  Has patch:  0
Needs documentation:  0 |Needs tests:  0
Patch needs improvement:  0 |  Easy pickings:  0
  UI/UX:  0 |
+
 Hello,

 Was going from Django version 1.10.7 to 1.11.4 and my migrations were
 working in 1.10.7 and stopped in 1.11.4. All my migrations were migrated
 before the upgrade. I went back to 1.10.7 and it was working again. Going
 back to 1.11.4 same error.

 {{{
 Traceback (most recent call last):
   File "manage.py", line 10, in 
 execute_from_command_line(sys.argv)
   File "[...]/venv/lib/python2.7/site-
 packages/django/core/management/__init__.py", line 363, in
 execute_from_command_line
 utility.execute()
   File "[...]/venv/lib/python2.7/site-
 packages/django/core/management/__init__.py", line 355, in execute
 self.fetch_command(subcommand).run_from_argv(self.argv)
   File "[...]/venv/lib/python2.7/site-
 packages/django/core/management/base.py", line 283, in run_from_argv
 self.execute(*args, **cmd_options)
   File "[...]/venv/lib/python2.7/site-
 packages/django/core/management/base.py", line 330, in execute
 output = self.handle(*args, **options)
   File "[...]/venv/lib/python2.7/site-
 packages/django/core/management/commands/migrate.py", line 163, in handle
 pre_migrate_state =
 executor._create_project_state(with_applied_migrations=True)
   File "/[...]/venv/lib/python2.7/site-
 packages/django/db/migrations/executor.py", line 81, in
 _create_project_state
 migration.mutate_state(state, preserve=False)
   File "[...]/venv/lib/python2.7/site-
 packages/django/db/migrations/migration.py", line 92, in mutate_state
 operation.state_forwards(self.app_label, new_state)
   File "[...]/venv/lib/python2.7/site-
 packages/django/db/migrations/operations/fields.py", line 150, in
 state_forwards
 delay = not old_field.is_relation
 AttributeError: 'NoneType' object has no attribute 'is_relation'
 }}}

 When I look in the fields.py file I can see on the line 139 a function:

 {{{
 def state_forwards(self, app_label, state):
 new_fields = []
 old_field = None
 for name, instance in state.models[app_label,
 self.model_name_lower].fields:
 if name != self.name:
 new_fields.append((name, instance))
 else:
 old_field = instance
 state.models[app_label, self.model_name_lower].fields = new_fields
 # Delay rendering of relationships if it's not a relational field
 delay = not old_field.is_relation
 state.reload_model(app_label, self.model_name_lower, delay=delay)
 }}}

 Found out that it was crashing on 1 of the model fields that are not
 existing anymore in the database. I added a line to print the name of the
 model and field to find out what is causing the crash.

 If old_field = None then it is calling a method on empty variable and it
 throws and error.

 Added this line

 {{{
 print app_label + " " + self.model_name_lower + " " + self.name
 }}}

 {{{
 def state_forwards(self, app_label, state):
 new_fields = []
 old_field = None
 print app_label + " " + self.model_name_lower + " " + self.name
 for name, instance in state.models[app_label,
 self.model_name_lower].fields:
 if name != self.name:
 new_fields.append((name, instance))
 else:
 old_field = instance
 state.models[app_label, self.model_name_lower].fields = new_fields
 # Delay rendering of relationships if it's not a relational field
 delay = not old_field.is_relation
 state.reload_model(app_label, self.model_name_lower, delay=delay)
 }}}

 The Output was

 {{{
 cars video subtitle_url
 cars photos gear
 cars news tags
 Traceback (most recent call last):
   File "manage.py", line 10, in 
 execute_from_command_line(sys.argv)
   File "[...]/venv/lib/python2.7/site-
 packages/django/core/management/__init__.py", line 363, in
 execute_from_command_line
 utility.execute()
   File "[...]/venv/lib/python2.7/site-
 packages/django/core/management/__init__.py", line 355, in execute
 self.fetch_command(subcommand).run_from_argv(self.argv)
   File "[...]/venv/lib/python2.7/site-
 packages/django/core/management/base.py", line 283, in run_from_argv
 self.execute(*args, **cmd_options)
   File "[...]/venv/lib/python2.7/site-
 packages/django/core/management/base.py", line 330, in execute
 output = self.handle(*args, **options)
   File "[...]/venv/lib/python2.7/site-