borinquenkid opened a new pull request, #16583:
URL: https://github.com/apache/grails-core/pull/16583
## Problem
`UniqueConstraint` added a condition for a property of the unique group only
when its value was not `null`. A `null` group value dropped the property from
the query, so `language unique: 'country'` checked `new Language(language:
'en')` as `where language = 'en'` and rejected it because `('en', 'US')`
exists. The same happened for the `Requestmap` (`url unique: 'httpMethod'`) of
the issue and for a self-referencing `Folder` (`name unique: 'parent'`), where
a top level folder conflicted with a folder of the same name under any parent.
This is stricter than any reading of `null`: in SQL `null` values never
conflict, and if `null` is a value it conflicts only with another `null`. All
datastores were affected.
## Fix
A `null` group value now adds `isNull(property)` to the query, so `null` is
compared as a value: `('Root', null)` conflicts only with another top level
`Root`. Non null values, the handling of unsaved to-one group members and the
`DirtyCheckable` shortcut are unchanged. The shortcut already looks at every
group property, so changing a group value to `null` triggers validation.
## Behaviour change (who is affected)
Applications that relied on a `null` group value matching every row of the
constrained property now get a successful validation when the rows differ in
the group property. The old behaviour was a defect and has no replacement. The
upgrade guide gets a new `upgrading90x` page (and a `toc.yml` entry) with this
note, and the `unique` constraint reference states the null semantics.
## Tests
- `UniqueConstraintNullGroupValueSpec` (TCK, runs on every datastore that
registers the constraint, here Hibernate 7): the `Requestmap`, `Language` and
`Folder` shapes, several nullable group members, and changing a saved row's
group value. Skipped on the simple in-memory datastore of the TCK, which does
not register the `unique` constraint.
- `UniqueConstraintSpec` in `grails-datamapping-core-test` (simple in-memory
datastore with the constraint registered): a null group value, including a
subclass.
- Red before the fix, green after. `:grails-datamapping-core` (2175 tests)
and `:grails-datamapping-core-test` (664 tests) pass; so do all `*Unique*`
specs of `:grails-data-hibernate7-core`.
Fixes #14503
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