Description Tom Bailey 2011-11-08 04:34:45 EST

Build Identifier: 2.3.0

We are using glassfish 3.1.1 (with eclipselink 2.3.0) and are having a strange problem with the cache on the entity manager.
Basically we want to detach entities before sending them to subsystems. It is the case (quite often) that the same entity can be changed twice within one transaction (by two different subsystems) and this multiple update of detached entities seems to expose an issue with the entity manager cache.
A simple example that exposes the problem is in the code below:
DataObject dataObject = entityManager.find(DataObject.class, dataObjectId);
entityManager.clear();
// First update
dataObject.setNotes("Notes 1");
entityManager.merge(dataObject);
// Simulate query implicit flush
entityManager.flush();
// Re-retrieve the entity
dataObject = entityManager.find(DataObject.class, dataObjectId);
// Detach again
entityManager.clear();
// Next update
dataObject.setNotes("Notes 2");
entityManager.merge(dataObject);
This code when run many times will alternately persist "Notes 1" to the database followed by "Notes 2" followed by "Notes 1" etc. However, if the code is changed so that the number after Notes increments every time then the correct value is always persisted. Therefore, it looks like the cache isn't updated after the first merge, so if the second merge has the same value as the object in cache then no merge takes place (leaving "Notes 1" on the object being persisted to the database).
The reason for the flush is because a query between the two updates would invoke an implicit flush. Without the flush the problem does not occur, so the flush seems to clear the entity manager cache back to the original state, rather than the state flushed to the database.

Adding a cache evict fixes the code:
DataObject dataObject = entityManager.find(DataObject.class, dataObjectId);
entityManager.clear();
// First update
dataObject.setNotes("Notes 1");
entityManager.merge(dataObject);
entityManager.getEntityManagerFactory().getCache().evict(DataObject.class, dataObject.getId());
// Simulate query implicit flush
entityManager.flush();
// Re-retrieve the entity
dataObject = entityManager.find(DataObject.class, dataObjectId);
// Detach again
entityManager.clear();
// Next update
dataObject.setNotes("Notes 2");
entityManager.merge(dataObject);
but it makes the system a lot slower to run and adds a requirement that the developer remembers to do an evict after every merge

Reproducible: Always

Steps to Reproduce:
1.Run code in details above
2.Note the value in the database is Notes 2
3.Run the code in details above again
4.Note the value in the database is now Notes 1!