#22932: "makemigrations" generates circular dependencies
-------------------------------------+-------------------------------------
Reporter: humitos | Owner: nobody
Type: Bug | Status: closed
Component: Migrations | Version: master
Severity: Normal | Resolution: fixed
Keywords: circular | Triage Stage:
dependency, migrations, | Unreviewed
makemigrations | Needs documentation: 0
Has patch: 0 | Patch needs improvement: 0
Needs tests: 0 | UI/UX: 0
Easy pickings: 0 |
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Comment (by andrewgodwin):
This is unavoidable, as Django can't detect swappable dependencies to
resolve the loop at makemigrations time (thanks, swappable models!), but
I've added some documentation to the custom user model docs to highlight
that this might occur and how to fix it.
The fix, incidentally, is to manually uncircularise the dependency loop.
In this example, the dependency graph is:
{{{
team.TeamCaptain -> challenge.MyUser -> team.Team
\_________________________^
}}}
As you can see, this isn't actually circular, it's just that the start and
end are in the same app and Django can't work out what app the middle one
is in (as it's dynamic and can change based on project settings). The
solution is to move the `TeamCaptain` model into a second migration in the
`team` app, and make sure the migration dependencies are modified
appropriately (i.e. that the `AUTH_USER_MODEL` dependency is also moved to
that second migration). This will solve this case.
The other possible case is when there actually is a dependency loop (e.g.
two models have foreign keys pointing at each other). You can resolve this
by splitting one ForeignKey off into a separate migration; just construct
this situation without swappable models and run `makemigrations` and
you'll get an example of how it's done.
--
Ticket URL: <https://code.djangoproject.com/ticket/22932#comment:3>
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