#12337: save_m2m() does not honor save_instance's exclude argument
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Reporter: margieroginski | Owner: melinath
Type: Bug | Status: new
Component: Forms | Version: SVN
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Changes (by melinath):
* owner: nobody => melinath
* status: reopened => new
* component: Database layer (models, ORM) => Forms
Comment:
Just ran across this myself. My use case looks like this:
{{{
class MyOtherModel(Model):
pass
class MyThroughModel(Model):
other = models.ForeignKey(MyOtherModel)
model = models.ForeignKey('MyModel')
# Plus some metadata fields that are handled automatically.
class MyModel(Model):
m2m = ManyToManyField(MyOtherModel, through=MyThroughModel)
class MyForm(ModelForm):
m2m = ModelMultipleChoiceField(queryset=MyOtherModel.objects.all())
class Meta:
model = MyModel
exclude = ('m2m',)
def save(self, commit=True):
# ... special behavior to handle the field.
}}}
With this setup, I am trying to exclude the default generated field and
its behavior. In this example, the {{{m2m}}} field name is used in both
the model definition and the form definition to represent a queryset of
{{{MyOtherModel}}} instances.
However, I could theoretically exclude the field and put a !CharField in
its place. The current save_m2m code would then blindly try to assign the
value of that !CharField to the m2m field on the model.
This is because rather than explicitly checking whether the field is being
excluded, the code assumes that if the field's name is in the
cleaned_data, it was not excluded. This is not consistent with how fields
and exclude are handled elsewhere in the codebase (for example in
construct_instance).
As far as I can tell, this would have fit well in
[https://github.com/django/django/commit/64ea5af1c992232f944ef403935d9cce316498bf
64ea5af/r8756], which added exclude support to the then-save_instance
function. My guess is that it was left out as an oversight rather than
intentionally.
--
Ticket URL: <https://code.djangoproject.com/ticket/12337#comment:9>
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