Hibernate 8 + Jakarta Persistence 4: EntityAgent and stateless sessions demo

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_017ic4b7jUQrypvpE1ix1k7V

output/01-entitymanager-vs-entityagent.txt

@@ -0,0 +1,13 @@
+EntityManager: find, edit title, commit (2 statements)
+  select b1_0.isbn,b1_0.price,b1_0.publisher_id,b1_0.title,b1_0.version,b1_0.views from book b1_0 where b1_0.isbn=?
+  select version from final table (update book set price=?,publisher_id=?,title=?,version=?,views=? where isbn=? and version=?)
+title in database afterwards: Changed via EntityManager
+
+EntityAgent: get, edit title, commit (1 statement)
+  select b1_0.isbn,b1_0.price,b1_0.publisher_id,b1_0.title,b1_0.version,b1_0.views from book b1_0 where b1_0.isbn=?
+title in database afterwards: Book 2
+
+EntityAgent: get, edit title, update(book), commit (2 statements)
+  select b1_0.isbn,b1_0.price,b1_0.publisher_id,b1_0.title,b1_0.version,b1_0.views from book b1_0 where b1_0.isbn=?
+  select version from final table (update book set version=case when price is distinct from ? or publisher_id is distinct from ? or title is distinct from ? then ? else version end,price=?,publisher_id=?,title=?,views=? where isbn=? and version=?)
+title in database afterwards: Changed via EntityAgent + update()

output/02-get-find-and-no-cache.txt

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+agent.find(missing)  -> null
+agent.get(missing)   -> EntityNotFoundException
+
+EntityAgent, same id twice in one transaction:
+  same instance? false
+  SQL (2 statements)
+  select b1_0.isbn,b1_0.price,b1_0.publisher_id,b1_0.title,b1_0.version,b1_0.views from book b1_0 where b1_0.isbn=?
+  select b1_0.isbn,b1_0.price,b1_0.publisher_id,b1_0.title,b1_0.version,b1_0.views from book b1_0 where b1_0.isbn=?
+
+EntityManager, same id twice in one transaction:
+  same instance? true
+  SQL (1 statement)
+  select b1_0.isbn,b1_0.price,b1_0.publisher_id,b1_0.title,b1_0.version,b1_0.views from book b1_0 where b1_0.isbn=?
+
+agent.getMultiple(3 ids) returned 3 books
+  SQL (1 statement)
+  select b1_0.isbn,b1_0.price,b1_0.publisher_id,b1_0.title,b1_0.version,b1_0.views from book b1_0 where b1_0.isbn in (?,?,?)

output/03-lazy-associations-and-fetch.txt

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+agent.get(Book): publisher initialized? false
+book.publisher.getName() before fetch -> LazyInitializationException
+agent.fetch(book.publisher) -> getName() = Manning
+  same object as book.publisher? true, initialized now? true
+  reading the public field p.name instead -> null
+  SQL (1 statement)
+  select p1_0.id,p1_0.name from publisher p1_0 where p1_0.id=?
+
+agent.get(Publisher): books collection initialized? false
+agent.fetch(publisher.books) -> 3 books
+  SQL (1 statement)
+  select b1_0.publisher_id,b1_0.isbn,b1_0.price,b1_0.title,b1_0.version,b1_0.views from book b1_0 where b1_0.publisher_id=?

output/04-bulk-insert.txt

@@ -0,0 +1,13 @@
+EntityManager.persist x 5000 in one transaction
+  entities held in the persistence context at the end: 5000
+  entity inserts: 5000   statements prepared: 1
+
+EntityAgent.insert x 5000 in one transaction
+  entities held anywhere: 0 (a StatelessSession has no persistence context)
+  entity inserts: 5000   statements prepared: 5000
+
+EntityAgent.insertMultiple(list of 5000)
+  entity inserts: 5000   statements prepared: 1
+
+publisher.id before insert: null
+publisher.id after insert:  1 (insert() itself returns void)

output/05-lock-modes-in-entityagent.txt

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+=== H2 ===
+
+get(Book.class, "978-1", OPTIMISTIC)
+  right after get() (1 statement)
+  select b1_0.isbn,b1_0.price,b1_0.publisher_id,b1_0.title,b1_0.version,b1_0.views from book b1_0 where b1_0.isbn=? for update
+  during commit (0 statements)
+  version before: 0, after: 0
+
+get(Book.class, "978-1", OPTIMISTIC_FORCE_INCREMENT)
+  right after get() (2 statements)
+  select b1_0.isbn,b1_0.price,b1_0.publisher_id,b1_0.title,b1_0.version,b1_0.views from book b1_0 where b1_0.isbn=? for update
+  update book set version=? where isbn=? and version=?
+  during commit (0 statements)
+  version before: 0, after: 1
+
+get(Book.class, "978-1", PESSIMISTIC_WRITE)
+  right after get() (1 statement)
+  select b1_0.isbn,b1_0.price,b1_0.publisher_id,b1_0.title,b1_0.version,b1_0.views from book b1_0 where b1_0.isbn=? for update
+  during commit (0 statements)
+  version before: 1, after: 1
+
+get(Book.class, "978-1", PESSIMISTIC_FORCE_INCREMENT)
+  right after get() (2 statements)
+  select b1_0.isbn,b1_0.price,b1_0.publisher_id,b1_0.title,b1_0.version,b1_0.views from book b1_0 where b1_0.isbn=? for update
+  update book set version=? where isbn=? and version=?
+  during commit (0 statements)
+  version before: 1, after: 2
+
+=== HSQLDB ===
+
+get(Book.class, "978-1", OPTIMISTIC)
+  FAILED: org.hibernate.HibernateException: Stateless optimistic locking requires transaction-long row protection; no strategy established for HSQLDialect:2:LOCKING
+
+get(Book.class, "978-1", OPTIMISTIC_FORCE_INCREMENT)
+  FAILED: java.lang.NullPointerException: Cannot invoke "Object.getClass()" because "owner" is null
+
+get(Book.class, "978-1", PESSIMISTIC_WRITE)
+  right after get() (1 statement)
+  select b1_0.isbn,b1_0.price,b1_0.publisher_id,b1_0.title,b1_0.version,b1_0.views from book b1_0 where b1_0.isbn=? for update
+  during commit (0 statements)
+  version before: 0, after: 0
+
+get(Book.class, "978-1", PESSIMISTIC_FORCE_INCREMENT)
+  FAILED: java.lang.NullPointerException: Cannot invoke "Object.getClass()" because "owner" is null
+

output/06-excluded-from-versioning.txt

@@ -0,0 +1,3 @@
+loaded: version=0 views=0
+after update() that changed only views: version=0 views=42
+after update() that changed title:     version=1 views=42

output/07-programmatic-result-set-mapping.txt

@@ -0,0 +1,5 @@
+entity mapping through EntityAgent: 3 rows, first = 978-1 / Book 1 / 10.00
+entity mapping through EntityManager: 3 rows, managed by the persistence context? true
+
+constructor mapping -> BookSummary[title=Book 1, price=10.00]
+tuple mapping -> (978-1, 0)

output/08-upsert-delete-and-errors.txt

@@ -0,0 +1,11 @@
+createEntityAgent() returns: org.hibernate.internal.StatelessSessionImpl
+instanceof org.hibernate.StatelessSession: true
+
+upsert(theme=dark) on an existing row, upsert(language=en) on a new row (2 statements)
+  merge into setting as t using (select cast(? as varchar(255)) name,cast(? as varchar(255)) val) as s on (t.name=s.name) when not matched then insert (name,val) values (s.name,s.val) when matched then update set val=s.val
+  merge into setting as t using (select cast(? as varchar(255)) name,cast(? as varchar(255)) val) as s on (t.name=s.name) when not matched then insert (name,val) values (s.name,s.val) when matched then update set val=s.val
+theme    -> dark
+language -> en
+
+insert() with an existing primary key -> jakarta.persistence.EntityExistsException
+find() after delete() -> null

output/09-same-operations-two-databases.txt

@@ -0,0 +1,12 @@
+=== H2 ===
+EntityAgent.update(stale book)      -> org.hibernate.HibernateException: The database returned no natively generated values : com.ankurm.agent.Book
+EntityManager.merge(stale book)     -> jakarta.persistence.OptimisticLockException
+EntityAgent.update(row not in db)   -> org.hibernate.HibernateException: The database returned no natively generated values : com.ankurm.agent.Book
+EntityAgent.upsert(new versioned)   -> org.hibernate.HibernateException: The database returned no natively generated values : com.ankurm.agent.Book
+
+=== HSQLDB ===
+EntityAgent.update(stale book)      -> jakarta.persistence.OptimisticLockException
+EntityManager.merge(stale book)     -> jakarta.persistence.OptimisticLockException
+EntityAgent.update(row not in db)   -> jakarta.persistence.OptimisticLockException
+EntityAgent.upsert(new versioned)   -> jakarta.persistence.OptimisticLockException
+