[borinquenkid]

Fixes #16700. Stacked on #16750 (it builds on the shared join table uniqueness of #16701 and the Db2 rules of #16750); retarget to 8.0.x once those merge.

Problem

Two unidirectional hasMany lists (or maps) to the same class that share one join table could not be saved:

NULL not allowed for column "ROLES_IDX"; SQL statement:
insert into owner_role (owner_deny_roles_id, deny_roles_idx, role_id) values (?, ?, ?)

Hibernate keys the join table of a list or a map with a primary key over its key and index columns (IndexedCollection.createPrimaryKey). On a shared table the next collection replaces it with its own, and it makes those columns NOT NULL, while a row of one list leaves the other list's columns null.

Change

SharedJoinTableUniqueKeyBinder, for each list or map of a shared table: makes its key and index columns nullable, drops that primary key, and gives it a uniqueness of its own over its key and index columns through SharedJoinTableUniqueness, the same per-database rules sets get:

Database	Two lists with a key column each	Two lists with one shared key column
H2, PostgreSQL, MySQL, MariaDB	a unique key per list	a unique key per list
Oracle, Db2 LUW	a unique key per list	one unique key over the key column and both index columns
Db2 for IBM i and z/OS	—	a create unique where not null index per list
SQL Server	—	a filtered unique index per list

A position or a map key is taken once; an element may repeat, as a list allows. On Oracle and Db2 LUW SharedJoinTableUniqueness now creates the key when there is none to widen, since a list has no implicit unique key (a set always has one, so sets are unchanged).

Tests

• SharedJoinTableListHibernate7Spec (new): both shapes keep their lists in order; removing from one list keeps the other and the order of the rest; an element may repeat and clearing one list keeps the other; two maps keep their entries. A container feature writes and reads both shapes on H2, PostgreSQL, MySQL, MariaDB, Oracle and Db2 (CI, amd64), and checks that a second row at a taken position is rejected; with the uniqueness removed every database accepts it.
• SharedJoinTableUniqueKeyBinderSpec: the DDL of two shared lists on H2, Oracle, Db2 LUW, IBM i and SQL Server (55/0).
• Full grails-data-hibernate7-core suite locally: 4293 tests, 0 failures (the shared DatabaseContainers of Hibernate 7: support Db2 in unique key null handling, regular expressions and native SQL reading #16750 makes the Oracle rows pass locally too).

Not covered: a set that shares a join table with a list.

Docs

The shared join table note of the 8.0.x upgrade guide, with the migration a schema created by an earlier Grails 8 release needs (drop the primary key, make the index columns nullable; dbCreate: update changes neither), and the one-to-many chapter.

https://claude.ai/code/session_01MDHn7fC3hsGJ27vFHD2o1p

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[borinquenkid]

CI run 40132431052 is green, with its tests run (run ci plus a ready toggle). SharedJoinTableListHibernate7Spec's container row passed on H2, Postgres, MySQL, MariaDB, Oracle and Db2 in all three Hibernate 7 test jobs that ran it.

[jamesfredley]

Not approving. Lists and maps that share a table can be inserted, but two lists that also share the element column still load and delete each other's rows.

[borinquenkid]

Resolved the row collision when collections share both foreign-key and element columns:

• For lists and maps sharing join tables, SharedJoinTableUniqueKeyBinder restricts each collection using its index column (and unshared element columns, if any). This ensures that collections sharing foreign-key and element columns isolate their rows by their distinct index columns (roles_idx is not null vs deny_roles_idx is not null).
• Loads, single-element removals, and bulk deletes now affect only the target collection's rows.
• Added tests verifying element ordering, single-element removal, and list-clearing isolation when two lists share both key and element columns.
• Updated documentation in the one-to-many chapter and the 8.0 upgrade guide.

[jamesfredley]

The earlier comment is fixed. Each shared list is restricted by its own index column, clearing one keeps the other, and loading no longer selects the other list's rows. That thread is resolved. Not approving yet, only because the migration steps leave an existing table unable to take rows from the other list.

[testlens-app]

✅ All tests passed ✅

🏷️ Commit: a99fd4b
▶️ Tests: 74301 executed
⚪️ Checks: 89/89 completed

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[jamesfredley]

Approving. The upgrade note now says to drop the primary key and make the owner-key and index columns nullable, which is what the binder does. That comment is resolved.