#24201: order_with_respect_to GenericForeignKey
-------------------------------------+-------------------------------------
Reporter: Alex Hill | Owner: nobody
Type: New feature | Status: closed
Component: Database layer | Version:
(models, ORM) |
Severity: Normal | Resolution: fixed
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
-------------------------------------+-------------------------------------
Comment (by Ashley Waite):
Replying to [comment:16 Simon Charette <charette.s@…>]:
> In [changeset:"c0118ff80bd14fe0f65843e5df266ec5d922304d" c0118ff8]:
> {{{
> #!CommitTicketReference repository=""
revision="c0118ff80bd14fe0f65843e5df266ec5d922304d"
> Refs #24201 -- Ignored order_with_respect_to private fields in
migrations.
>
> Thanks Tim for the review.
> }}}
This commit removes the {{{order_with_respect_to}}} option during
migration state if it's a generic foreign key.
I can see why this was done, as private fields are not present on the
model state, so it cannot be resolved.
However, as the option is removed, no {{{_order}}} field is created in the
database and no {{{AlterOrderWithRespectTo}}} operations can be generated
for the migration either.
An {{{AlterOrderWithRespectTo}}} operation cannot be manually added either
because the migrations {{{ModelState}}} does not copy private fields
either, so attempting to add it results in referring to a field it cannot
find.
Manually adding an {{{AlterOrderWithRespectTo}}} operation referring to
another field will result in it being removed in any subsequent migration.
When you attempt to use the model it hard breaks because there's no
{{{_order}}} field in the database.
{{{
psycopg2.ProgrammingError: column test_model._order does not exist
django.db.utils.ProgrammingError: column test_model._order does not exist
}}}
This requires several changes in the migration module to resolve
_correctly_, but can be hackishly bypassed by replacing
[[https://github.com/django/django/blob/c0118ff80bd14fe0f65843e5df266ec5d922304d/django/db/migrations/state.py#L446-L448|state.py#446-448]]
with:
{{{
# Private fields are ignored, so remove options that refer to
them.
elif options.get('order_with_respect_to') in (field.name for field
in model._meta.private_fields):
options['order_with_respect_to'] = model._meta.pk.attname
}}}
Which leads to the creation of {{{_order}}} and
{{{AlterOrderWithRespectTo}}} operations, thinking that it's ordering
according to the {{{id}}} field, but as it migrates and functions
successfully, this is the clear source of why it currently breaks.
--
Ticket URL: <https://code.djangoproject.com/ticket/24201#comment:17>
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