#33192: It is not possible to use a custom lookup/transorm in a CheckConstraint
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Reporter: Fabien MICHEL | Owner: nobody
Type: Bug | Status: closed
Component: Database layer | Version: 3.1
(models, ORM) | Resolution:
Severity: Normal | worksforme
Keywords: lookup, transform, | Triage Stage:
CheckContraint, migrate | 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 Simon Charette):
> In this case, won't I expose my migration to use code that could be
ananchronic if the code of the custom lookup changes after the migration
has been created? Is it not better to embed the custom lookup on the
migration which create the constraint in database ?
The migration framework doesn't detect change at the resulting SQL level
so if you were to change your lookup logic you'd have to manually create a
migration that removes and adds back the new constraint. Nothing prevents
you from defining the lookup in two locations though (`ready()`) and in
the migration itself so it's already there and only overrides the project
specific lookup when the migration file is loaded. Just keep in mind that
Django won't be hand holding you if you change the SQL generated by the
lookup.
In a sense this is similar to how Django allows you to add and remove
managers to your model definition without 'baking' the manage definition
in the migration file; since the migration framework holds 'references' of
managers and lookups it's your responsibility to keep 'referenced values'
coherent with migration states.
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Ticket URL: <https://code.djangoproject.com/ticket/33192#comment:8>
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