LuciferYang opened a new pull request, #10291:
URL: https://github.com/apache/paimon/pull/10291
### Purpose
Altering the element type (or element nullability) of a `MULTISET` column
threw a misleading `ColumnNotExistException`: the nested type-update walk in
`NestedSchemaUtils` had no `MULTISET` case, so an off-by-one routed the change
to `updateLastColumn` on an empty list. A `MULTISET<T>` is physically stored as
`InternalMap<T, Int>`, so the element is a map key, and the read-side cast
infrastructure (`SchemaEvolutionUtil`) has no MULTISET executor and
`createMapCastExecutor` deliberately forbids changing a map key type. So a
multiset element type change cannot be applied to existing data.
This rejects a multiset element modification at DDL time with a clear,
actionable message ("Cannot update the element type of MULTISET column ... a
multiset element is a map key, whose type cannot be evolved") instead of the
misleading `ColumnNotExistException`. The `MULTISET` column's own top-level
nullability change (the column, not its element) is unaffected and keeps
working.
This closes #10290.
### Tests
- `NestedSchemaUtilsTest` asserts that changing a multiset element type,
element nullability, or a complex multiset element is rejected with the clear
message (`testMultisetElementTypeChangeRejected`,
`...NullabilityChangeRejected`, `...OfComplexTypeRejected`).
- `testMultisetTypeUpdateNullability` pins that the multiset column's own
nullability change still applies.
### API and Format
No.
### Documentation
No.
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