#36652: Django Squashed Migrations Randmonly Passing/Failing Based On Set
Iteration
Order
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Reporter: Jayden Kneller | Type: Bug
Status: new | Component: Migrations
Version: dev | Severity: Normal
Keywords: | Triage Stage: Unreviewed
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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This could be a duplicate of many other projects, but I've figured out a
bug fix that may also solve the issues of the other projects.
I've created a github repo that contains a project with migrations,
squashed migrations, and a management command. If someone checks out the
repo and runs the `showmigrations` management command multiple times, the
results will pass or fail in a way that appears random.
https://github.com/arrai-innovations/django-migrationnames
I've tracked the issue down to the order that a set is iterated over. If
that set is turned into a list, without any other code changes, the issue
shown in this test project stops failing and instead passes 100% of the
time. I can't guarrantee it will fix every other users issues with
circular dependency errors, but it will stop the randomness that is
happening because of iterating through a set.
If someone uses the management command I created, called `show_issue`, it
will create output with a number of files that contain results parsed from
the patched `MigrationLoader`. The data comes from
`loader.graph.node_map`, where the migrations and their children are
stored. In essence, there are 8 different possibilities that the
migrations and children can be figured out as, because of the set. 2 of
these 8 possibilities pass and the other 6 cause circular dependency
errors. The fix changes things to have 1 possibility for the way
migrations and children are figured out, and it passes.
The randomness of iterating over the set and having 8 possible
migration/children setups is what makes things difficult to deal with when
working with squashed migrations.
I've written about the management command and how to use it in the
README.md of the django-migrationnames project.
The fix is really small, which I have in a fork. Since it is very small,
this is the change:
https://github.com/jayden-
arrai/django/commit/fceaa5820edfbd7128082e7d199034963ae6cd33
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Ticket URL: <https://code.djangoproject.com/ticket/36652>
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