#34881: migrate crashes when renaming model referenced twice by
ManyToManyField.through model on SQLite.
----------------------------+----------------------------------------
Reporter: dennisvang | Owner: Jase Hackman
Type: Bug | Status: assigned
Component: Migrations | Version: dev
Severity: Normal | Resolution:
Keywords: sqlite | Triage Stage: Accepted
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
----------------------------+----------------------------------------
Comment (by Simon Charette):
Thanks for working on this patch during DjangConUS Jase!
From reviewing your changes and tests I get a sense that there might be an
even less invasive way to address this particular issue.
The crux of the problem here, as you've identified it, is the SQLite
backend needs to rebuild the table entirely and it cannot be done from an
old representation of the model iteratively.
By the time `alter_field` is called the columns of the tables related to
the one being renamed are already altered in the database (a `RENAME`
operation repoints all referencing columns) so it should be safe to
provide the model originating from `to_state`
[https://github.com/django/django/blob/fdd1323b9c83e56184e0c992af8faf8d54327775/django/db/migrations/operations/models.py#L421
like we do when dealing with self-referencing related objects].
By retrieving the model meant to be passed to `alter_field` from to
`to_state`
{{{#!diff
diff --git a/django/db/migrations/operations/models.py
b/django/db/migrations/operations/models.py
index d616cafb45..83e3fb772d 100644
--- a/django/db/migrations/operations/models.py
+++ b/django/db/migrations/operations/models.py
@@ -421,11 +421,11 @@ def database_forwards(self, app_label,
schema_editor, from_state, to_state):
model = new_model
related_key = (app_label, self.new_name_lower)
else:
- model = related_object.related_model
related_key = (
related_object.related_model._meta.app_label,
related_object.related_model._meta.model_name,
)
+ model = to_state.apps.get_model(*related_key)
to_field =
to_state.apps.get_model(*related_key)._meta.get_field(
related_object.field.name
)
}}}
The tests seem to be passing.
I think that your work on `alter_fields` might be beneficial to support
tickets like #24203 but might not be strictly necessary to address this
particular issue.
--
Ticket URL: <https://code.djangoproject.com/ticket/34881#comment:17>
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