#31767: Strange behaviour with QuerySet unions with ModelMultipleChoiceField
---------------------------------------+------------------------
Reporter: Tom Carrick | Owner: nobody
Type: Bug | Status: new
Component: Forms | Version: master
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 |
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I came across this issue on Stack Overflow. I'm not 100% sure it's a bug,
but it does seem strange. With this code (excuse the bizarre example
filtering):
{{{
class Publication(models.Model):
pass
class Article(models.Model):
publications = models.ManyToManyField(to=Publication, blank=True,
null=True)
class ArticleForm(forms.ModelForm):
publications = forms.ModelMultipleChoiceField(
Publication.objects.filter(id__lt=2) |
Publication.objects.filter(id__gt=5),
required=False,
)
class Meta:
model = Article
fields = ["publications"]
class ArticleAdmin(admin.ModelAdmin):
form = ArticleForm
}}}
This works well. However, changing the `ModelMultipleChoiceField` queryset
to use `union()` breaks things.
{{{
publications = forms.ModelMultipleChoiceField(
Publication.objects.filter(id__lt=2).union(
Publication.objects.filter(id__gt=5)
),
required=False,
)
}}}
The form correctly shows only the matching objects. However, if you submit
this form while empty (i.e. you didn't select any publications), ALL
objects matching the queryset will be added. Using the `OR` query, NO
objects are added, as I'd expect.
--
Ticket URL: <https://code.djangoproject.com/ticket/31767>
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