[I] [Hibernate 7] A unidirectional hasMany that shares a join table with another silently drops addTo* [grails-core]

["borinquenkid (via GitHub)" <gi...@apache.org>]

borinquenkid opened a new issue, #16699:
URL: https://github.com/apache/grails-core/issues/16699

   ### Expected Behavior
   
   An owner with two unidirectional `hasMany` to the same class that share one join table (no `joinTable` mapping)
   
   ```groovy
   class Item {
       static hasMany = [roles: Role, denyRoles: Role]
   }
   ```
   
   writes a role added to either collection to the join table, or fails the save with an error. `failOnError: true` must not pass while rows are dropped.
   
   ### Actual Behaviour
   
   On Hibernate 7 the classic domain binder keeps the rule from #10811 in `CollectionKeyColumnUpdater`: when the owner has more than one unidirectional to-many sharing the collection's join table, the key of each collection is made nullable **and not updatable**. Hibernate 7's collection persister writes no rows for a collection whose key is not updatable, so `addToRoles` and `addToDenyRoles` are both dropped silently and the collections reload empty, even with `failOnError: true`.
   
   #16686 keeps the key updatable for collections with join tables of their own (the reporter's first shape in #16665) and leaves this shared-table case as it was. This issue is the follow-up it points to.
   
   ### Analysis
   
   - A local probe by @jdaugherty on #16686 made the key always updatable: both collections of `hasMany = [roles: Role, denyRoles: Role]` were written to the shared table and read back correctly, and the `hasmany` package and the specs of #16686 still passed. So the #10811 rule may not be needed on Hibernate 7 at all, as the reporter suggested in #16665.
   - The native domain generator of the 9.x branches already treats the rule as a defect rather than a rule to copy and always makes the key updatable (see the javadoc of `GrailsDomainGenerator.collectionKeyFacets`), so dropping it on 8.x brings the classic binder in line with native binding.
   - What needs a look before dropping it: the shared join table has three columns (`item_id`, `item_roles_id`, `item_deny_roles_id`) but the classic binder's unique key covers only the **first** collection's key column with the element column, `UNIQUE (item_roles_id, item_id)`. Rows of the second collection leave `item_roles_id` null. H2 creates the key `NULLS DISTINCT`, but databases that treat nulls as equal in a unique constraint (SQL Server, for example) would reject two `denyRoles` rows for the same role from different owners. Either the unique key has to cover every key column of the table, or each collection needs a unique key of its own, or the binder should give each collection its own join table by default.
   
   ### Steps To Reproduce
   
   Register the `Item`/`Role` classes above against the Hibernate 7 datastore of 8.0.x, add a role to each collection, flush, clear the session and reload: both collections are empty. `MultipleUnidirectionalHasManySpec` (from #16686) has the per-collection join table shape; the shared-table shape is `CKCUSharedTableOwner` in `CollectionKeyColumnUpdaterSpec`, which currently asserts the key is not updatable.
   
   ### Environment Information
   
   - Grails 8.0.x, `grails-data-hibernate7`, classic domain binding.
   
   Related: #16665, #16686, #10811.


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Re: [I] [Hibernate 7] A unidirectional hasMany that shares a join table with another silently drops addTo* [grails-core]

["borinquenkid (via GitHub)" <gi...@apache.org>]

borinquenkid commented on issue #16699:
URL: https://github.com/apache/grails-core/issues/16699#issuecomment-6387644778

   Fixed by #16701.


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