#35640 closed Bug (invalid)
ModelMultipleChoiceField fail when the foreignkey remote model is a child class of anohter model
Reported by: | Omar BENHAMID | Owned by: | |
---|---|---|---|
Component: | Forms | Version: | 3.2 |
Severity: | Normal | Keywords: | |
Cc: | Omar BENHAMID | Triage Stage: | Unreviewed |
Has patch: | yes | Needs documentation: | no |
Needs tests: | no | Patch needs improvement: | no |
Easy pickings: | no | UI/UX: | no |
Description (last modified by )
The issue
When a child model is used as a foreign key, forms with ModelMultipleChoiceField (not setting to_field_name) will systematically fail to validate submited values.
Reproduction
models.py
class A(models.Model): pass class B(A): pass class C(models.Model): fkfield = models.ForeignKey(B, on_delete=models.CASCADE)
Create form with MultipleChoiceField of the foreignkey fkfield and it will systematically fail to validate.
Reason
ModelMultipleChoiceField uses value.pk in prepare_value to generate choices but uses "to_field_name" in _check_data for validation.
default to_field_name is by default related_field.field_name which is "<parent>_ptr" in the case of inheriance child models, which points to the parent itself (not the pk).
ModelMultipleChoiceField fail when the foreignkey remote model is a child class of anohter model
Workaround
Use to_field_name = 'pk' when ModelMultipleChoiceField is created.
Proposed fix
Use PK in validation like in generation of choices.
Spotted in 3.2
Change History (4)
comment:1 by , 3 months ago
Description: | modified (diff) |
---|---|
Version: | 5.1 → 3.2 |
comment:2 by , 3 months ago
Resolution: | → invalid |
---|---|
Status: | new → closed |
comment:3 by , 3 months ago
There is indeed an issue, the question is the use cas support it : is it worth solving ?
Currently django-slick-report builds a search form using a ModelMultipleChoiceField backed by a simple ForeignKey field (the aim is to select mutliple values for an "OR-search"). The way values are genrated for the choices of the widgets are the same only if the field is iterable (so one to many but not many to one) and this often works well except when model inheritence is used.
This is exists in 5.1 and I can try to provide demo project but before is : is this usage supported ? Shall we try to make this part more robust in django?
comment:4 by , 3 months ago
My advice would be to create a discussin on the Django forum in the "Django Internals" category where other folks will be able to see the issue: https://forum.djangoproject.com/c/internals/
We'll be able to gauge whether it's worth fixing by the responses people give.
Sorry but 3.2 is no longer supported 🤷♂️