#36128: Document the necessity of adding unique constraints to related models in
intermediary m2m model.
-------------------------------------+-------------------------------------
Reporter: Guillaume LEBRETON | Owner: Clifford
| Gama
Type: Bug | Status: new
Component: Documentation | Version: 5.1
Severity: Normal | Resolution:
Keywords: | Triage Stage: Ready for
| checkin
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Changes (by Guillaume LEBRETON):
* resolution: fixed =>
* status: closed => new
Comment:
I'm sorry to not have taken a look while it was still open, but my point
was not so about the lack of integrity constraint on the example, but the
lack of proper validation when there is an integrity constraint.
I've looked at the patch and it just add a mention about the unique
constraint, but nothing about the validation.
If i add this uniqueness constraint, the result of adding a duplicate will
be an integrity error rather than a validation error, and the hassle is
writing a complex validation logic like this for a proper validation:
`admins.py`
{{{
class MembersFormset(forms.models.BaseInlineFormSet):
def clean(self):
groups = []
for form in self.forms:
if form.cleaned_data:
groups.append((form.cleaned_data['group'],
form.cleaned_data['person']))
duplicated_groups = [x for x in groups if groups.count(x) > 1]
if duplicated_groups:
raise ValidationError(
'Duplicated values: %(duplicates)s',
params={'duplicates': ", ".join(group.__str__() for group
in set(duplicated_groups))}
)
class MembershipInline(admin.TabularInline):
model = Membership
extra = 1
formset = MembersFormset
}}}
Maybe i missed something, but i find the updated doc even more misleading
now, before the example was quite incomplete because there is almost
always a need for unique constraint in m2m models, but now the provided
example is not working properly because of failing validation.
--
Ticket URL: <https://code.djangoproject.com/ticket/36128#comment:10>
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