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

## Quickstart

```bash
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](docs/01-get-vs-load.md) |
| `mergerefresh` | `merge()` vs `refresh()` against a `@Version`-ed entity | [docs/02-merge-vs-refresh.md](docs/02-merge-vs-refresh.md) |
| `insert-identity` | Batch insert attempt with `GenerationType.IDENTITY` | [docs/03-inserting-objects.md](docs/03-inserting-objects.md) |
| `insert-sequence` | The same insert, with `GenerationType.SEQUENCE` | [docs/03-inserting-objects.md](docs/03-inserting-objects.md) |

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

## Regenerating captured output

```bash
./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](docs/00-versions.md) | Verified version pins, and the Spring Boot patch that silently changes which Hibernate patch you get |
| [01 — get() vs load()](docs/01-get-vs-load.md) | Proxy deferral, `LazyInitializationException`, proxy identity vs `equals()` |
| [02 — merge() vs refresh()](docs/02-merge-vs-refresh.md) | Optimistic locking, which method fails loudly vs silently |
| [03 — Inserting objects](docs/03-inserting-objects.md) | `IDENTITY` vs `SEQUENCE` and JDBC batching, with `hibernate.generate_statistics` as evidence |

## Captured output index

| File | Scenario |
|---|---|
| [docs/output/get-vs-load.txt](docs/output/get-vs-load.txt) | `getvsload` |
| [docs/output/merge-vs-refresh.txt](docs/output/merge-vs-refresh.txt) | `mergerefresh` |
| [docs/output/insert-identity.txt](docs/output/insert-identity.txt) | `insert-identity` |
| [docs/output/insert-sequence.txt](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](LICENSE).