#11811: No error raised on update(foreignkey=unsavedobject) on nullable fk
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Reporter: Afief | Owner: ashearer
Status: assigned | Milestone: 1.2
Component: Database layer (models, ORM) | Version: 1.1
Resolution: | Keywords:
Stage: Accepted | Has_patch: 0
Needs_docs: 0 | Needs_tests: 0
Needs_better_patch: 0 |
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Comment (by ashearer):
The same surprising behavior occurs whether you assign to the ForeignKey
field by attribute assignment, a model initializer,
model.objects.create(), or queryset.update(). In any of the cases, passing
an unsaved model acts the same as passing None. (That's assuming no manual
pk assignment.) The first three use a different code path than the last.
I'm attaching a strawman patch that will raise a ValueError with a helpful
message in all four cases. The docs had left the behavior undefined.
However, the patch needs further work:
1. Raising an exception at assignment time may be a bad idea, even though
the inconsistency between my_fk_field (an object) and my_fk_field_id
(None) starts then. Everything would have worked OK while the same object
remained in memory; only the copy saved in the DB will have no link at all
to the other instance. Checking at save time may be better.
2. To match the scope of the ticket, I'm only handling assignment for
non-null fields. Non-nullable fields already raise an exception, though it
occurs later (on save), and the error message is less specific as a
result. But the queryset.update() code path now always throws the new
exception regardless of whether the field is nullable, because field
information isn't available to it.
3. Two tests of multi-DB support now fail, because they make the same
mistake the new exception is designed to guard against. Either putting
explicit IDs in the tests or changing the timing of the exceptions as per
point 1 may help. The rest of the test suite has no additional failures.
The patch includes tests but not docs. I'll attach a docs patch separately
once the implementation settles down.
--
Ticket URL: <http://code.djangoproject.com/ticket/11811#comment:3>
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