[Django] #30460: ManyToMany relationships with a custom `through` do not respect Meta.ordering on the intermediary model
Django
Meta.ordering on the intermediary model
-------------------------------------+-------------------------------------
Reporter: | Owner: nobody
ryanpetrello |
Type: Bug | Status: new
Component: Database | Version: 2.2
layer (models, ORM) |
Severity: Normal | Keywords:
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
-------------------------------------+-------------------------------------
`ManyToManyField`s that specify an intermediary model with a custom
`Meta.ordering` do not inherit that ordering.
{{{#!python
class Dog(models.Model):
pass
class OrderedMembership(models.Model):
class Meta:
ordering = ('position',)
dog = models.ForeignKey('Dog', models.CASCADE)
winner = models.ForeignKey('Winner', models.CASCADE)
position = models.PositiveIntegerField()
class Winner(models.Model):
name = models.CharField(max_length=128)
# OrderedMembership object defined as a class
members = models.ManyToManyField(Dog, through=OrderedMembership)
lassie = Dog('Lassie')
fido = Dog('Fido')
rover = Dog('Rover')
dog_show = Winner(name='Dog Show')
OrderedMembership.objects.create(dog=lassie, winner=dog_show, position=3)
OrderedMembership.objects.create(dog=fido, winner=dog_show, position=2)
OrderedMembership.objects.create(dog=rover, winner=dog_show, position=1)
dog_show.members.all() # <--- does not respect
`OrderedMembership.position`
}}}
This means that if you want to create a custom M2M model that manages
default order via some column on the M2M table:
https://github.com/ansible/awx/pull/3842/files#diff-
ea6da88b8c0cd3fbf7858ae87933b296R995
https://github.com/gregmuellegger/django-
sortedm2m/blob/b48481ebd1212f1af22a6a04d1c8372b5a837350/sortedm2m/fields.py#L41
...it doesn't work as you'd expect (the M2M relation falls back to natural
database order - usually the primary key of the target model).
--
Ticket URL: <https://code.djangoproject.com/ticket/30460>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
Django
Meta.ordering on the intermediary model
-------------------------------------+-------------------------------------
Type: New feature | Status: new
Component: Database layer | Version: 2.2
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 1
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
* needs_better_patch: 0 => 1
* has_patch: 0 => 1
* type: Bug => New feature
* stage: Unreviewed => Accepted
Comment:
I wouldn't say this is actually a bug as many-to-many field managers have
always supported ordering on their referenced model
Adding support for `through._meta.ordering` has backward compatibility
concerns as we have to decide how to deal with `ordering` defined on both
the `through` and `to` model. Should the `through` ordering have
precedence over the `to`ordering? Should they be merged together? We also
have to make sure whatever we do regarding ordering translation honors the
mechanisms in place to exclude `Meta.ordering` from aggregation as naively
translating it into an `order_by` call will bypass the checks added in
1b1f64ee5a78cc217fead52cbae23114502cf564 for #14357.
In my opinion the resulting ordering should be `through._meta.ordering` +
`to._meta.ordering`. This might require a django-developers thread to
gather feedback though.
Accepting the ticket on the basis that it seems like a feature that should
be supported but the current PR requires significant adjustments first.
--
Ticket URL: <https://code.djangoproject.com/ticket/30460#comment:1>
Django
Meta.ordering on the intermediary model
-------------------------------------+-------------------------------------
Type: New feature | Status: new
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Needs tests: 0 | Patch needs improvement: 1
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
* version: 2.2 => master
--
Ticket URL: <https://code.djangoproject.com/ticket/30460#comment:2>
Django
Meta.ordering on the intermediary model
-------------------------------------+-------------------------------------
Type: New feature | Status: new
Component: Database layer | Version: master
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Needs tests: 0 | Patch needs improvement: 1
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Comment (by Baptiste Mispelon):
I just closed #17344 as a duplicate. It was older but there wasn't much
discussion on that ticket so I figured I would keep this one open instead.
I'll also note that there's #17345 which is partially related (being able
to define an explicit ordering without using a through table).
--
Ticket URL: <https://code.djangoproject.com/ticket/30460#comment:3>
Django
Meta.ordering on the intermediary model
-------------------------------------+-------------------------------------
Type: New feature | Status: new
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Needs tests: 0 | Patch needs improvement: 1
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Comment (by mnieber):
I just found out that you can use
`dog_show.members.all().order_by('orderedmembership')`. However, afaik,
this (surprising!) feature is not documented, would be nice to add this to
the docs.
--
Ticket URL: <https://code.djangoproject.com/ticket/30460#comment:4>
Django
Meta.ordering on the intermediary model
-------------------------------------+-------------------------------------
Type: New feature | Status: new
Component: Database layer | Version: dev
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Needs tests: 0 | Patch needs improvement: 1
-------------------------------------+-------------------------------------
* cc: Ülgen Sarıkavak (added)
--
Ticket URL: <https://code.djangoproject.com/ticket/30460#comment:5>
Django
Meta.ordering on the intermediary model
-------------------------------------+-------------------------------------
Type: New feature | Status: new
Component: Database layer | Version: dev
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Needs tests: 0 | Patch needs improvement: 1
-------------------------------------+-------------------------------------
* cc: Dmytro Litvinov (added)
--
Ticket URL: <https://code.djangoproject.com/ticket/30460#comment:6>