[Django] #23739: django 1.7.1 defer() throws AttributeError when using related_name
Django
-------------------------+-------------------------------------------------
Reporter: | Owner: nobody
farhan85 | Status: new
Type: | Version: 1.7
Uncategorized | Keywords: defer related_name AttributeError
Component: | RelatedObject rel
Uncategorized | Has patch: 0
Severity: Normal | UI/UX: 0
Triage Stage: |
Unreviewed |
Easy pickings: 0 |
-------------------------+-------------------------------------------------
I have attached a simple example project, with the following Models
defined:
{{{
#!python
class ModelA(models.Model):
name = models.CharField(max_length=255)
class ModelB(models.Model):
name = models.CharField(max_length=255)
model_a = models.ForeignKey(ModelA, related_name='model_b')
}}}
Entering the following code (in a Django shell) works fine:
{{{
#!python
ModelB.objects.filter(name='').select_related('model_a').defer('model_a__name')
}}}
But when I run the following:
{{{
#!python
ModelA.objects.filter(name='').select_related('model_b').defer('model_b__name')
}}}
I get this error message:
{{{
Traceback (most recent call last):
File "<console>", line 1, in <module>
File "/home/fahammed/Documents/django_defer_bug/venv/local/lib/python2.7
/site-packages/django/db/models/query.py", line 116, in __repr__
data = list(self[:REPR_OUTPUT_SIZE + 1])
File "/home/fahammed/Documents/django_defer_bug/venv/local/lib/python2.7
/site-packages/django/db/models/query.py", line 141, in __iter__
self._fetch_all()
File "/home/fahammed/Documents/django_defer_bug/venv/local/lib/python2.7
/site-packages/django/db/models/query.py", line 966, in _fetch_all
self._result_cache = list(self.iterator())
File "/home/fahammed/Documents/django_defer_bug/venv/local/lib/python2.7
/site-packages/django/db/models/query.py", line 222, in iterator
only_load = self.query.get_loaded_field_names()
File "/home/fahammed/Documents/django_defer_bug/venv/local/lib/python2.7
/site-packages/django/db/models/sql/query.py", line 1821, in
get_loaded_field_names
self.deferred_to_data(collection, self.get_loaded_field_names_cb)
File "/home/fahammed/Documents/django_defer_bug/venv/local/lib/python2.7
/site-packages/django/db/models/sql/query.py", line 596, in
deferred_to_data
cur_model = source.rel.to
AttributeError: 'RelatedObject' object has no attribute 'rel'
}}}
Looks like defer doesn't work when you specify the related table using its
{{{related_name}}}.
--
Ticket URL: <https://code.djangoproject.com/ticket/23739>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
Django
Reporter: farhan85 | Owner: nobody
Type: Bug | Status: new
Component: Database layer | Version: 1.7
(models, ORM) | Resolution:
Severity: Normal | Triage Stage:
Keywords: defer related_name | Unreviewed
AttributeError RelatedObject rel | Needs documentation: 0
Has patch: 0 | Patch needs improvement: 0
Needs tests: 0 | UI/UX: 0
Easy pickings: 0 |
-------------------------------------+-------------------------------------
Changes (by farhan85):
* needs_better_patch: => 0
* type: Uncategorized => Bug
* component: Uncategorized => Database layer (models, ORM)
* needs_tests: => 0
* needs_docs: => 0
--
Ticket URL: <https://code.djangoproject.com/ticket/23739#comment:1>
Django
Reporter: farhan85 | Owner: nobody
Type: Bug | Status: new
Component: Database layer | Version: 1.7
(models, ORM) | Resolution:
Keywords: defer related_name | Needs documentation: 0
AttributeError RelatedObject rel | Patch needs improvement: 0
Has patch: 0 | UI/UX: 0
Needs tests: 0 |
Easy pickings: 0 |
-------------------------------------+-------------------------------------
Changes (by timgraham):
* severity: Normal => Release blocker
* stage: Unreviewed => Accepted
Comment:
This seems to be a regression present since 1.6 -- bisected to
70679243d1786e03557c28929f9762a119e3ac14. Test for Django's test suite
attached.
--
Ticket URL: <https://code.djangoproject.com/ticket/23739#comment:2>
Django
Reporter: farhan85 | Owner: nobody
Cleanup/optimization | Version: 1.7
Component: Database layer | Resolution:
(models, ORM) | Triage Stage: Accepted
Severity: Normal | Needs documentation: 0
Keywords: defer related_name | Patch needs improvement: 0
AttributeError RelatedObject rel | UI/UX: 0
Has patch: 0 |
Needs tests: 0 |
Easy pickings: 0 |
-------------------------------------+-------------------------------------
* type: Bug => Cleanup/optimization
* severity: Release blocker => Normal
Comment:
The reason pre-1.6 didn't raise exceptions was that the chunked reads
implementation swallowed exceptions. I don't think there is a regression
here, we just get an exception instead of silently returning empty list on
error.
I tested this on Django 1.5 with the following command: `[o for o in
ModelB.objects.filter(name='').select_related('model_b').defer('model_b__name').iterator()]`.
This raises a different error (ModelB has no field named 'model_b'), but
doesn't produce any results.
We might want to allow usage of `related_name` in this context, and even
if we don't, users shouldn't get such an ugly error message.
--
Ticket URL: <https://code.djangoproject.com/ticket/23739#comment:3>
Django
Reporter: farhan85 | Owner: nobody
Type: | Status: new
Cleanup/optimization | Version: 1.7
Component: Database layer | Resolution:
(models, ORM) | Triage Stage: Accepted
Severity: Normal | Needs documentation: 0
Keywords: defer related_name | Patch needs improvement: 0
AttributeError RelatedObject rel | UI/UX: 0
Has patch: 0 |
Needs tests: 0 |
Easy pickings: 0 |
-------------------------------------+-------------------------------------
Comment (by farhan85):
@akaariai That's not the code that was causing the error message. From
{{{ModelB.objects.filter(name='')}}}, you select the related objects from
''ModelA'' and then defer the {{{ModelA.name}}} value from the DB. So your
command should probably be:
{{{#!python
[o for o in
ModelB.objects.filter(name='').select_related('model_a').defer('model_a__name').iterator()]
}}}
Note that {{{ModelB}}} has no field called {{{model_b}}}} but it does have
a field called {{{model_a}}}.
--
Ticket URL: <https://code.djangoproject.com/ticket/23739#comment:4>
Django
Reporter: farhan85 | Owner: nobody
Type: | Status: new
Cleanup/optimization | Version: 1.7
Component: Database layer | Resolution:
(models, ORM) | Triage Stage: Accepted
Severity: Normal | Needs documentation: 0
Keywords: defer related_name | Patch needs improvement: 0
AttributeError RelatedObject rel | UI/UX: 0
Has patch: 0 |
Needs tests: 0 |
Easy pickings: 0 |
-------------------------------------+-------------------------------------
Comment (by akaariai):
I'm confused. Using `[o for o in
ModelA.objects.filter(name='').select_related('model_b').defer('model_b__name')]`
gives me RelatedObject has no attribute rel in 1.5. Just as it does using
master. And, `[o for o in
ModelB.objects.filter(name='').select_related('model_a').defer('model_a__name').iterator()]`
works on master.
--
Ticket URL: <https://code.djangoproject.com/ticket/23739#comment:5>
Django
Reporter: farhan85 | Owner: nobody
Type: | Status: new
Cleanup/optimization | Version: 1.7
Component: Database layer | Resolution:
(models, ORM) | Triage Stage: Accepted
Severity: Normal | Needs documentation: 0
Keywords: defer related_name | Patch needs improvement: 0
AttributeError RelatedObject rel | UI/UX: 0
Has patch: 0 |
Needs tests: 0 |
Easy pickings: 0 |
-------------------------------------+-------------------------------------
Comment (by farhan85):
I think that's because the attribute {{{model_a}}} has been explicitly
defined in the class definition of {{{ModelB}}}, whereas the class
definition of {{{ModelA}}} does not have an attribute called
{{{model_b}}}. Correct me if I'm wrong, but the {{{ModelA.model_b}}} is
dynamically created at runtime (or loaded when the value is called)?
On another (possibly) similar note, calling the {{{only()}}} function:
{{{#!python
ModelA.objects.filter(name='').select_related('model_b').only('model_b__name')
}}}
also returns the same error {{{AttributeError: 'RelatedObject' object has
no attribute 'rel'}}}, and the following line works fine:
{{{#!python
ModelB.objects.filter(name='').select_related('model_a').only('model_a__name')
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/23739#comment:6>
Django
Reporter: farhan85 | Owner: nobody
Cleanup/optimization |
Component: Database layer | Version: 1.7
(models, ORM) |
Keywords: defer related_name | Triage Stage: Accepted
AttributeError RelatedObject rel |
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Changes (by timgraham):
* status: new => closed
* resolution: => invalid
Comment:
The problem seems to be an invalid `select_related()` query. On Django
1.9:
{{{
>>>
ModelA.objects.filter(name='').select_related('model_b').defer('model_b__name')
django.core.exceptions.FieldError: Invalid field name(s) given in
select_related: 'model_b'. Choices are: (none)
}}}
You should be using `prefech_related()` when querying reverse foreign
keys.
--
Ticket URL: <https://code.djangoproject.com/ticket/23739#comment:7>