jamesfredley commented on issue #14935:
URL: https://github.com/apache/grails-core/issues/14935#issuecomment-3930840467
scenario (from `exampleAppSimple2` / `exampleAppGrails700M5`):
1. Create + update entity - DB version=1
2. Load `ds1` (v=1) and `ds2` (v=1) in separate sessions
3. Update via `ds1` - DB version=2
4. Try update via `ds2` - correctly gets `OptimisticLockingFailureException`
(v=1 vs DB v=2)
5. Call `ds2.merge()` expecting an attached copy with DB's version=2 and
their `name` change applied
6. Gets `ds2Copy.version == 1` (detached version) - eventual
`OptimisticLockingException` at flush
## Why This Is Expected
GORM's `performMerge()` is a straight pass-through to Hibernate's
`session.merge()` with no custom version handling:
```groovy
// AbstractHibernateGormInstanceApi.groovy
protected D performMerge(final D target, final boolean flush) {
hibernateTemplate.execute { Session session ->
Object merged = session.merge(target)
session.lock(merged, LockMode.NONE)
if (flush) { flushSession(session) }
return (D) merged
}
}
```
Hibernate 5.6's `DefaultMergeEventListener.entityIsDetached()` does exactly
this:
```java
// 1. Load entity from DB
final Object result = source.get(entityName, clonedIdentifier); // version=2
// 2. Check version mismatch
else if (isVersionChanged(entity, source, persister, target)) {
throw new StaleObjectStateException(entityName, id); // Fires here
}
// 3. Only if versions match: copy state
copyValues(persister, entity, target, source, copyCache);
```
`merge()`
- Copies **ALL state** from detached to managed (including version)
- Uses the version specifically for **conflict detection**
- Throws immediately if versions don't match
The correct pattern for "load fresh + apply my changes" is:
```groovy
Example.withNewTransaction {
Example fresh = Example.get(ds2.id) // version=2 from DB
fresh.name = ds2.name // apply only desired changes
fresh.save() // succeeds
}
```
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