#33313: Inheriting from multiple abstract models with same field causes name
collision when overriding field is direct parent
-------------------------------------+-------------------------------------
Reporter: Ben Nace | Owner: nobody
Type: Bug | Status: new
Component: Database | Version: 3.2
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 |
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Given the following example models:
{{{
class ModelActivation(models.Model):
start_date = models.DateField(null=True, blank=True)
end_date = models.DateField(null=True, blank=True)
active = models.BooleanField()
class Meta:
abstract = True
class BaseData(ModelActivation):
entity_state = models.CharField(max_length=100)
class Meta:
abstract = True
class RequiredStart(models.Model):
start_date = models.DateField()
class Meta:
abstract = True
class RequiredEnd(models.Model):
end_date = models.DateField()
class Meta:
abstract = True
class RequiredStartEnd(RequiredStart, RequiredEnd):
class Meta:
abstract = True
}}}
\\
Any of the following when the override for start_date is defined on a
direct parent model, results in the error "(models.E006) The field
'start_date' clashes with the field 'start_date' from model
'app.testmodel' (or 'app.testmodel2')"
{{{
class TestModel(RequiredStart, BaseData):
pass
class TestModel2(RequiredStart, ModelActivation):
pass
}}}
However, if the overriding field is pushed up to a grandparent model,
rather than a direct parent, it works fine.
{{{
class TestModel3(RequiredStartEnd, BaseData):
pass
class TestModel4(RequiredStartEnd, ModelActivation):
pass
}}}
In my limited debugging, it appears to me that this is because of the way
inherited_attributes is tracked in the __new__ method of the ModelBase
model metaclass (in django.db.models.base.py). For a grandparent model,
not being a direct parent, all items in the __dict__ will be added to
inherited_attributes, which includes the fields:
{{{
if base not in parents or not hasattr(base, '_meta'):
# Things without _meta aren't functional models, so
they're
# uninteresting parents.
inherited_attributes.update(base.__dict__)
continue
}}}
However, when a field is inherited from a direct parent, it is not added
to inherited_attributes, it is not added to field_names, and it does not
appear in new_class.__dict__, so the field from the ancestor higher up in
the mro is also added via
{{{
for field in parent_fields:
if (field.name not in field_names and
field.name not in new_class.__dict__ and
field.name not in inherited_attributes):
new_field = copy.deepcopy(field)
new_class.add_to_class(field.name, new_field)
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/33313>
Django <https://code.djangoproject.com/>
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