#28862: Removing a field from index_together/unique_together and from the model
generates a migration that crashes
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Reporter: Artem Maslovskiy | Owner: Jeff
Type: Bug | Status: assigned
Component: Migrations | Version: 1.9
Severity: Normal | Resolution:
Keywords: models migrations | Triage Stage: Accepted
Has patch: 1 | 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 had a look at the issue and I came to the conclusion that the only
solution for now is to disable `AlterFooTogether` optimization when a
`RemoveField` on the same model is involved.
As mentioned by Ramiro we'd need to have access to the ''previous''
`foo_together` value to determine whether or not the optimization can take
place. This is a class of problem that also came up when working on #27768
where I had to disable an optimization from taking place because I didn't
have the ''previous'' context of a `RemoveField`.
I guess I'd be possible to have newly generated operation embed a such a
''previous'' state to allow the optimization to take place but I figured
out what I believe is a clever way of working around this disabled
optimization. By implementing `CreateModel`/`AlterFooOperation` reduction
most of the negative side effect during migration squashing where the
optimizer perform a complete reduction are gone because the former is able
to reduce `RemoveField` operation.
All of these ideas are implemented in this
[https://github.com/django/django/pull/10178 PR].
--
Ticket URL: <https://code.djangoproject.com/ticket/28862#comment:22>
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