#22837: Migrations detect unnessecary(?) changes
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Reporter: valberg | Owner: nobody
Type: Uncategorized | Status: closed
Component: Migrations | Version: 1.7-beta-2
Severity: Normal | Resolution: invalid
Keywords: | Triage Stage: Unreviewed
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 MarkusH):
Replying to [comment:3 pykler]:
> Tell me what the correct behaviour is in the following scenario
(according to the ticket close comment, this is a scenario that is
designed for).
>
> {{{
> 0001 migration choices are ('a', 'apple'), ('b', 'banana')
> 0002 data insert into table choice 'banana'
> 0003 migration model has only one choice now ('a', 'apple')
> }}}
>
> From my tests, django doesn't (and 100% defenitely shouldn't) be
deleting data or replacing data in every record of my database table on
migration 0003. So the reality is, this point in time validation check is
really only for checking if the choice is valid during the data migration
which isn't really useful.
Django will **not** go through your database table and remove all rows
with 'banana'. But you could add another migration that selects all rows
that don't have valid data and work with them on your own. And you can
only do that if you have `choices` in your field definition.
> The problem with this design is some apps (third party) will have a
dynamic set of choices depending on your settings, so they cannot reliably
deliver a set of migrations causing the user of the app to have to create
migrations on behalf of the third party app.
They can, by passing a callable to `choices`. See #13181
--
Ticket URL: <https://code.djangoproject.com/ticket/22837#comment:4>
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