✅ Short Answer
Session.refresh(entity) reloads the state of a persistent entity from the database, overwriting any in-memory changes with the latest data in the database.
🔎 Detailed Explanation
- When you load an entity into a Hibernate session, Hibernate keeps it in its first-level cache (persistence context).
- If the entity’s data is modified outside Hibernate (e.g., by another application or direct SQL), your in-memory object can become stale.
- Calling
session.refresh(entity)forces Hibernate to:- Execute a SELECT query to reload the entity’s current state from the database.
- Overwrite the in-memory fields of the entity with fresh database values.
- Leave the entity in the persistent state (still tracked by the session).
- Important: Any unsaved changes you made in memory to the entity will be discarded.
📅 When to Use Session.refresh()
✅ When you suspect the database has changed outside your Hibernate session (e.g., direct SQL updates, other systems modifying the same record).
✅ To ensure your application is using the latest data, especially in high-concurrency environments.
✅ Before performing logic that depends on up-to-date values (e.g., checking a current balance before transferring funds).
🧑💻 Code Example
Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();
MyEntity entity = session.get(MyEntity.class, 1L);
System.out.println("Old value: " + entity.getName());
// Imagine another app updates this row in the DB at this point
session.refresh(entity); // Forces SELECT to reload latest state
System.out.println("Refreshed value: " + entity.getName());
tx.commit();
session.close();
📊 Quick Comparison with Similar Methods
| Method | Purpose |
|---|---|
session.flush() | Syncs in-memory changes → database |
session.refresh() | Syncs database → in-memory object |
💡 Extra Insight: refresh() vs. lock()
refresh()actively reloads data from the DB, overwriting local state.lock(entity, LockMode.NONE)reattaches a detached entity without querying the DB (no refresh of data).
📌 Key Takeaways
✅ Session.refresh(entity) reloads an entity from the database, overwriting local changes.
✅ Use it to ensure you have the latest data, especially when other systems or transactions might change the database.
✅ Be careful: any unsaved local changes to the entity will be lost after refresh.