#24542: Inheriting from multiple abstract model base classes with the same field
leads to invalid SQL and db-level exception
-------------------------------------+-------------------------------------
Reporter: Ghopper21 | Owner: nobody
Type: Bug | Status: new
Component: Database layer | Version: 1.6
(models, ORM) | Keywords: multiple model
Severity: Normal | inheritance sql fielderror
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Given the following model classes:
{{{
class Daddy(models.Model):
class Meta:
abstract = True
foobar = models.CharField(default="", max_length=20)
class Mommy(models.Model):
class Meta:
abstract = True
foobar = models.CharField(default="", max_length=20)
class Kid(Daddy, Mommy):
pass
}}}
Django will validate this. However, the foobar field will show up twice in
Kid._meta.local_fields, and if you try to save a Kid model instance,
Django will generate SQL code that references foobar twice, leading to a
hard-to-debug database level exception.
I suggest expected behavior to be either (1) throw a FieldError on
validation (consistent with what Django does if a child model tries to
"hide" a parent's field) or (2) ignore subsequent model fields from
abstract model base classes (per MRO-order) with the same name as existing
fields.
The real-world context that led to this bug discovery: in refactoring a
large existing project, I subclassed models.Model and had all project
models inherit from this subclass, which added a new field (let's call it
foobar). Some models had multiple abstract base classes that subclassed
from models.Model, in a typical mixin pattern. Django was validating and
then creating foobar twice for such models, leading to the database error
due to invalid SQL.
--
Ticket URL: <https://code.djangoproject.com/ticket/24542>
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