#36652: Loading squashed migrations from disk raises CircularDependencyError
indeterministically
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Reporter: Jayden Kneller | Owner: Augusto Pontes
Type: Bug | Status: assigned
Component: Migrations | Version: dev
Severity: Normal | Resolution:
Keywords: squashed | Triage Stage: Accepted
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 Jayden Kneller):
So, after getting the test project down to 3 apps and 7 total migrations,
I've tracked the issue down to the order that
`self.graph.remove_replaced_nodes(key, migration.replaces)` gets called,
which is determined by the order of `self.replacements.items()`, which is
determined by the order of `migration_names`. If the second migration in
app_one is added to `self.replacements` before the first migration, since
dictionaries are now ordered by default, then a cyclic dependency error
occurs 100% of the time. To confirm this you can rename migration
`0002_squashed_initial` to `0000_squashed_initial` and call `show_issue
--use-fixed`.
If it is possible to mock the results that `self.replacements.items()`
returns, then I we could have a test that guarantees the results of either
a pass or CircularDependencyError based on the order of the migrations we
return, but with the migration names being a set right now, that mock
would still be susceptible to it only giving the result we want 50% of the
time. So, how do we write a test that will fail if the migration names is
a set?
Or, perhaps a better fix than making the migration names into a list,
would be for self.replacements to be added to in the order that migrations
would run. But, I'm not sure how easy that would be.
Any ideas for how to do a test?
--
Ticket URL: <https://code.djangoproject.com/ticket/36652#comment:24>
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