#28188: Field._get_default prevents model fields from being pickled
-----------------------------------------+------------------------
Reporter: Adam Alton | Owner: nobody
Type: Uncategorized | Status: new
Component: Uncategorized | Version: 1.11
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
-----------------------------------------+------------------------
The changes introduced in
[[https://github.com/django/django/commit/d2a26c1a90e837777dabdf3d67ceec4d2a70fb86
#diff-
bf776a3b8e5dbfac2432015825ef8afe|d2a26c1a90e837777dabdf3d67ceec4d2a70fb86]]
mean that in cases where a model field has a default and the default is
not a callable, the field instance cannot be pickled.
The offending line is:
{{{#!python
return lambda: self.default
}}}
This problem only exists in Django version >= 1.11.
The reason for that ''lambda'' is because the code has been refactored so
that all the logic for getting the default value has been moved into the
''_get_default'' method, which allows it to be cached with the
''@cached_property'' decorator. And then the ''get_default'' method
expects the value returned from ''_get_default'' to always be a callable.
That requirement for the value to always be a callable is the reason for
wrapping the value with ''lambda'' in the case where it's not already a
callable.
My proposed solution is to simply move the ''if callable()'' check back
out into the ''get_default'' method. This would mean that we lose a very
minor bit of efficiency because we have to run that one ''if'' statement
each time that ''get_default'' is called, but the rest of the logic would
remain inside the cached ''_get_default'' method.
I have made a commit here which contains my proposed fix and a test to
prevent regression:
https://github.com/adamalton/django/commit/a7c3f672d2ea45df2fdea8cad6ffcfa10172b133
--
Ticket URL: <https://code.djangoproject.com/ticket/28188>
Django <https://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 unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
To view this discussion on the web visit
https://groups.google.com/d/msgid/django-updates/052.6a741c4fc01a20d4329236aaf4d5ebb7%40djangoproject.com.
For more options, visit https://groups.google.com/d/optout.
