#31416: FieldError when migrating field to new model subclass.
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Reporter: Eduard Anghel | Owner: Nan Liu
Type: Bug | Status: assigned
Component: Migrations | Version: master
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by Simon Charette):
I think it should be doable to teach the auto-detector about generating
these operations in the right order.
I think the best approach would be to adjust `check_dependency` to account
for this case. What's happening now is that created models detection runs
before removed models one so while both operations depend on `Readable`
model. It's possible that `generate_created_models` might need to be
adjusted to add a dependency on field removal of all of its base to make
sure the order is swapped. I think the correct dependency representation
is `(base_app_label, base_model_name, field_name, False)` for all fields
in all bases in
https://github.com/django/django/blob/6fbce45b0376f0ec8f3bf244f4f1f8d62c201f58/django/db/migrations/autodetector.py#L561-L565.
Something the solution has to consider is when a field is removed from a
base while two subclasses are added in the same run with this field (e.g.
an extra `class Magazine(Readable): title =
models.CharField(max_length=200)` would be added to the reporter's
example). In this case a single `RemoveField` must be generated
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Ticket URL: <https://code.djangoproject.com/ticket/31416#comment:6>
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