[Django] #24547: Errors for paths for Model relationships in other apps can be misleading / confusing

Django

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Mar 27, 2015, 11:50:22 AM3/27/15

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#24547: Errors for paths for Model relationships in other apps can be misleading /
confusing
--------------------------------------+------------------------------------
Reporter: akulakov | Owner: nobody
Type: Cleanup/optimization | Status: new
Component: Migrations | Version: master
Severity: Normal | Keywords: error message, warning
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 1 | UI/UX: 0
--------------------------------------+------------------------------------
If a user is creating a relationship to a model in another app, it would
be natural to use a path like: ForeignKey('app2.models.Model2'). This is
consistent with e.g. urlconf where views are referenced like
'myapp.views.my_view', or generally django imports that use dots to
separate elements of a full path.

The error you would get looks like this:
app2.M1.f3: (fields.E300) Field defines a relation with model
'app3.models.M1', which is either not installed, or is abstract.

It might seem like it's not a big deal -- user just has to look at the
docs or google for the error.

However, in some cases it may lead to some loss of time, for example I had
circular foreign key dependencies between models for testing and thought
the error is due to circular references. More generally, django errors can
result from seemingly unrelated causes so if a user starts with a firm
assumption that a full path needs to be given, the error might lead them
to look for all kinds of workarounds to try before coming back to the path
format.

It would be easy for django to check the path and, if there are more than
one dot in path, and specifically if '.models.' is included in path, a
hint should be shown along with the error:

> NOTE: path should be of the form 'myapp.MyModel' and should NOT include
the name of module containing models (which is usually 'models').

--
Ticket URL: <https://code.djangoproject.com/ticket/24547>
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Django

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Mar 27, 2015, 11:56:43 AM3/27/15

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#24547: Errors for paths for Model relationships in other apps can be misleading /
confusing

* needs_better_patch: => 0
* component: Migrations => Database layer (models, ORM)
* needs_tests: => 0
* easy: 1 => 0
* needs_docs: => 0
* stage: Unreviewed => Accepted

--
Ticket URL: <https://code.djangoproject.com/ticket/24547#comment:1>

Django

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Mar 27, 2015, 12:58:42 PM3/27/15

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#24547: Errors for paths for Model relationships in other apps can be misleading /
confusing

-------------------------------------+-------------------------------------
Reporter: akulakov | Owner: akulakov
Type: | Status: assigned

Changes (by akulakov):

* owner: nobody => akulakov
* status: new => assigned

--
Ticket URL: <https://code.djangoproject.com/ticket/24547#comment:2>

Django

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Apr 2, 2015, 12:57:07 PM4/2/15

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#24547: Errors for paths for Model relationships in other apps can be misleading /
confusing

Comment (by akulakov):

I no longer get the error in description, instead I get this traceback:

{{{
File "/Users/akulakov/projects/testproj/app1/models.py", line 4, in
<module>
class M1(models.Model):
File "/Users/akulakov/projects/django/django/db/models/base.py", line
158, in __new__
new_class.add_to_class(obj_name, obj)
File "/Users/akulakov/projects/django/django/db/models/base.py", line
294, in add_to_class
value.contribute_to_class(cls, name)
File
"/Users/akulakov/projects/django/django/db/models/fields/related.py", line
1819, in contribute_to_class
super(ForeignObject, self).contribute_to_class(cls, name,
virtual_only=virtual_only)
File
"/Users/akulakov/projects/django/django/db/models/fields/related.py", line
299, in contribute_to_class
lazy_related_operation(resolve_related_class, cls,
self.remote_field.model, field=self)
File
"/Users/akulakov/projects/django/django/db/models/fields/related.py", line
80, in lazy_related_operation
return apps.lazy_model_operation(partial(function, **kwargs),
*model_keys)
File
"/Users/akulakov/projects/django/django/db/models/fields/related.py", line
78, in <genexpr>
model_keys = (make_model_tuple(m) for m in models)
File "/Users/akulakov/projects/django/django/db/models/utils.py", line
13, in make_model_tuple
app_label, model_name = model.split(".")
ValueError: too many values to unpack (expected 2)
}}}

So it looks like this was changed and the original error can no longer be
triggered?

Unless there's some circumstances that can trigger the original error (I
couldn't find any -- tried both creating initial migration, creating a new
table, adding to existing table), this ticket should be closed.

--
Ticket URL: <https://code.djangoproject.com/ticket/24547#comment:3>

Django

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Apr 7, 2015, 12:01:35 PM4/7/15

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#24547: Errors for paths for Model relationships in other apps can be misleading /
confusing

-------------------------------------+-------------------------------------
Reporter: akulakov | Owner: akulakov

Type: | Status: closed

Cleanup/optimization |
Component: Database layer | Version: master

(models, ORM) | Resolution:
Severity: Normal | worksforme