#7623: Multi-table inheritance does not allow linking new instance of child
model
to existing parent model instance.
-------------------------------------+-------------------------------------
Reporter: brooks.travis@… | Owner: nobody
Type: Bug | Status: reopened
Component: Database layer | Version: SVN
(models, ORM) | Resolution:
Severity: Normal | Triage Stage: Design
Keywords: model-inheritance, | decision needed
multi-table-inheritance | Needs documentation: 1
Has patch: 1 | Patch needs improvement: 1
Needs tests: 1 | UI/UX: 0
Easy pickings: 0 |
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Changes (by akaariai):
* cc: anssi.kaariainen@… (added)
Comment:
If you want to extend an existing instance, you need to copy all fields of
the parent to the new child manually. Unfortunately this can't be done in
a generic way using only public APIs. Although ._meta is semi-public and
doing
{{{
child = ChildModel(**childfields) # set child field values
for field in parent._meta.fields:
setattr(child, field.attname, getattr(parent, field.attname)) # set
child values from parent
child.parent_ptr = parent.pk # not sure if this is strictly necessary,
probably so...
}}}
or something along those lines should work (not tested). Now, I don't
think this can be officially documented without making ._meta.fields part
of the public API. I would have use for a helper method that does this.
--
Ticket URL: <https://code.djangoproject.com/ticket/7623#comment:18>
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