hibernate-demo/README.md

hibernate-demo

Companion repository for three ankurm.com posts on Hibernate 7's persistence-context APIs: get() vs load()/getReference(), merge() vs refresh(), and inserting objects efficiently. Every claim in those posts that comes from this repo traces to a script here and a captured transcript in docs/output/ — nothing is asserted that wasn't actually run.

Versions

Component	Version
Hibernate ORM	7.4.1.Final (GA 2026-06-09)
Spring Boot	4.1.0 (GA 2026-06-10)
Java	25 (LTS)
H2	in-memory, managed by Spring Boot

See docs/00-versions.md for how these were verified and a trap worth knowing about if you bump the Spring Boot version.

Quickstart

git clone https://ankurm.com/git.app/asmhatre/hibernate-demo.git
cd hibernate-demo
./scripts/run.sh getvsload

Requires JDK 25 and a network connection the first time (Maven needs to fetch plugins online before -o offline mode works for subsequent runs).

Profiles

Each profile is a CommandLineRunner against an in-memory H2 database. There is no web server — every run starts, executes its scenario, prints the result, and exits.

Profile	Runs	Chapter
getvsload	session.get() vs session.getReference(), proxies, LazyInitializationException	docs/01-get-vs-load.md
mergerefresh	merge() vs refresh() against a @Version-ed entity	docs/02-merge-vs-refresh.md
insert-identity	Batch insert attempt with GenerationType.IDENTITY	docs/03-inserting-objects.md
insert-sequence	The same insert, with GenerationType.SEQUENCE	docs/03-inserting-objects.md

./scripts/run.sh getvsload
./scripts/run.sh mergerefresh
./scripts/run.sh insert-identity
./scripts/run.sh insert-sequence

Regenerating captured output

./scripts/run-all.sh

Regenerates every file in docs/output/ from a real run. scripts/clean_output.py strips JVM noise and a harmless duplicate SQL echo line so the committed transcripts stay readable — nothing else is edited by hand.

Documentation index

Chapter	Covers
00 — Versions	Verified version pins, and the Spring Boot patch that silently changes which Hibernate patch you get
01 — get() vs load()	Proxy deferral, LazyInitializationException, proxy identity vs equals()
02 — merge() vs refresh()	Optimistic locking, which method fails loudly vs silently
03 — Inserting objects	IDENTITY vs SEQUENCE and JDBC batching, with hibernate.generate_statistics as evidence

Captured output index

File	Scenario
docs/output/get-vs-load.txt	getvsload
docs/output/merge-vs-refresh.txt	mergerefresh
docs/output/insert-identity.txt	insert-identity
docs/output/insert-sequence.txt	insert-sequence

Layout

hibernate-demo/
├── pom.xml
├── LICENSE
├── scripts/
│   ├── run.sh              start one profile, run it, exit
│   ├── run-all.sh          regenerate every docs/output/ file
│   └── clean_output.py     strip JVM noise + a duplicate SQL echo line from a raw capture
├── src/main/java/com/ankurm/hibernatedemo/
│   ├── HibernateDemoApplication.java
│   ├── model/               Book, WidgetIdentity, WidgetSequence
│   └── scenario/            one CommandLineRunner per profile
└── docs/
    ├── 00-versions.md .. 03-inserting-objects.md
    └── output/*.txt         captured, unedited console transcripts

License

MIT — see LICENSE.