[release/7.0] Avoid circular dependency for unique indexes with null values #29921
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Port of #29796
Fixes #29647
Description
When SaveChanges performs the topological sort of the update commands it considers duplicate values for unique indexes as invalid and throws an exception. However, in many database providers duplicate
nullvalues are allowed for unique indexes.Customer impact
Affected apps throw during SaveChanges for duplicate
nullvalues. The workaround is to add a filter to every unique index in the model and then manually edit the migration to avoid rebuilding the indexes.How found
Multiple customer reports on 7.0
Regression
Yes.
Testing
Added tests for the affected scenario.
Risk
Medium; the fix considerably changes the implementation, but a quirk was added to revert back to older behavior.