#29896: Regression when saving a ForeignKey with to_field attr. Cached model is
lost.
-------------------------------------+-------------------------------------
Reporter: Maciej | Owner: nobody
Gol |
Type: Bug | Status: new
Component: Database | Version: 2.1
layer (models, ORM) |
Severity: Normal | Keywords:
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
-------------------------------------+-------------------------------------
Hey guys, during recent patching run I've encountered regression between
Django 2.0.9 and 2.1.2.
Given models:
{{{
class Author(models.Model):
username = models.CharField(primary_key=True)
numeric_id = models.AutoField()
class Book(models.Model):
author = models.ForeignKey(Author, on_delete=models.Cascade)
author_numeric = models.ForeignKey(Author, on_delete=models.Cascade,
to_field="numeric_id")
}}}
The following test fails, although it shouldn't.
{{{
class SomeTest(TestCase):
def
test_foreign_key_with_to_field_should_properly_persist_through_save(self):
author = Author.objects.create(username="yada")
book = Book(author=author, author_numeric=author)
book.save()
with self.assertNumQueries(0):
book.author_numeric # No queries below Django 2.1. One query
for Django 2.1.
}}}
The problem comes from the `save()` method here:
{{{
# If the relationship's pk was changed, clear the cached
# relationship.
if obj and obj.pk != getattr(self, field.attname):
field.delete_cached_value(self)
}}}
We compare `obj.pk` with `book.author_numeric_id`, but `pk` is a string
(`username`) and `author_numeric_id` is an integer. It should look for
`to_field` value, instead:
{{{
# If the relationship's pk was changed, clear the cached
# relationship.
if obj and getattr(obj, field.target_field.attname) !=
getattr(self, field.attname):
field.delete_cached_value(self)
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/29896>
Django <https://code.djangoproject.com/>
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