#26352: models.E003 check incorrectly prevents duplicate ManyToMany through-self
that differ by through_fields
-------------------------------------+-------------------------------------
Reporter: Simon Willison | Owner: nobody
Type: Bug | Status: new
Component: Database layer | Version: 1.9
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage:
| Unreviewed
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Changes (by Raymond Penners):
* status: closed => new
* resolution: wontfix =>
Comment:
This ticket got closed because of a missing use case. For what it is
worth, our "real world use case" is the following:
{{{#!python
class ShippingMethod(models.Model):
....
to_countries = models.ManyToManyField(
Country, through='carriers.ShippingMethodPrice',
through_fields=('method', 'to_country'))
# This is the 2nd ManyToManyField causing E003:
#
# from_countries = models.ManyToManyField(
# Country, through='carriers.ShippingMethodPrice',
# through_fields=('method', 'from_country'), related_name='+')
class ShippingMethodPrice(models.Model):
...
method = models.ForeignKey(
ShippingMethod,
related_name='prices'
)
to_country = models.ForeignKey(Country)
from_country = models.ForeignKey(Country, related_name='+')
price = models.DecimalField()
}}}
So, basically, we have list of shipping methods, and each shipping method
has a price list, containing a specific price per from/to-country
combination.
Given a method, `method.from_countries` should represent the set of all
countries that are occur in the price list as a from-country.
I do not think the workaround suggested in
https://code.djangoproject.com/ticket/26352#comment:2 works for us, as our
case involves 3 models.
The hack to disable E003 seems to work, though a real fix (or suggestions
how to receive the same result otherwise) would be appreciated.
--
Ticket URL: <https://code.djangoproject.com/ticket/26352#comment:6>
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