#13030: Natural Key deserialization fails on foreign key to field that is
itself a
foreign key
---------------------------+------------------------------------------------
Reporter: yishaibeeri | Owner: nobody
Status: new | Milestone:
Component: Serialization | Version: SVN
Keywords: natural keys | Stage: Unreviewed
Has_patch: 0 |
---------------------------+------------------------------------------------
Attached diff has a test showing this:
In (nonabstract) model inheritance, the child model's B primary key is not
the usual integer, but rather a FK to the parent A.
Suppose model B has defined natural_key() and get_by_natural_key().
If a third model C has a field that is a foreign key to B, loading it
using deserialization with natural keys will fail. During creation of the
C instance (let's call it objC), this is what happens:
* First, the natural key will be used to successfully construct the
instance of B (let's call it objB).
* Then, an assignment is made to set the relevant field of objC to point
to objB. However, instead of the naive {{{objC.thefield = objB}}}, the
actual assignment uses the relevant field.rel.field_name to do something
along the lines of:
{{{
field_name = field.rel.field_name
objC.thefield_id = getattr(objB, field_name)
}}}
* In the usual case where field_name is a simple primary key (such as
'id'), this works nicely. However,
* when this field is in itself a foreignkey, the result from getattr is
an object - the relevant objA(!). This of course throws a nasty exception.
I have not tried, but it appears this would fail in a similar fashion in
any case where the target of the first FK (from objC) is itself an FK and
not a simple field (even without involving inheritance).
Perhaps the naive approach ({{{objC.thefield = objB}}}) would work better
for all cases? This is a bit too deep for me, I'm afraid.
--
Ticket URL: <http://code.djangoproject.com/ticket/13030>
Django <http://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
--
You received this message because you are subscribed to the Google Groups
"Django updates" group.
To post to this group, send email to [email protected].
To unsubscribe from this group, send email to
[email protected].
For more options, visit this group at
http://groups.google.com/group/django-updates?hl=en.
