#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 pykler):
To me this is future proofing since no DBMS (that I know of) has such a
constraint on char fields (which is what is used here).
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.
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.
Surely there is a better design out there to solve the scenario where a
datamigration is somehow validated and no grief is caused to django users.
PS. I believe django migrations are very elegant even with this little
design snafu https://twitter.com/pykler/status/546868601492627456
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Ticket URL: <https://code.djangoproject.com/ticket/22837#comment:3>
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