# sdjpa4-demo

Companion code for the Spring Data JPA and transaction articles on **[ankurm.com](https://ankurm.com)**.

Two independent Maven modules under one aggregator:

| Module | Article(s) | Boot / JDK |
|---|---|---|
| [`migration-behavior/`](migration-behavior) | the four Spring Data JPA 3→4 migration articles | 4.0.6 / 21 |
| [`transactions/`](transactions) | [@Transactional: propagation, isolation and the six silent failures](https://ankurm.com/) | 4.1.1 / 25 |

The modules deliberately pin different Spring Boot versions. `migration-behavior` stays on
4.0.6 because that is what the four published migration articles were written and verified
against, and upgrading it would silently invalidate output those articles quote.

> **Moved in September 2026.** The migration project used to live at the repository root. It is
> now under `migration-behavior/`; source paths gained that prefix and nothing else changed. The
> `article-1-baseline`, `article-2-query-engine` and `article-3-advanced` tags still point at the
> original layout, so a link into a tagged tree is unaffected.

```bash
./mvnw -DskipTests package     # both modules
./mvnw test                    # every test in both
```

## Tags

- `article-1-baseline`, `article-2-query-engine`, `article-3-advanced` - the exact code each article quotes, frozen at publish time.
- `corner-scenarios` (and `main`) - the enriched, current state described below. Some method signatures have moved on from the article-tagged snapshots (e.g. `Book`'s `price` is now an embedded `Money` value object, not a bare `BigDecimal`), so check out the matching article tag if you want the code to line up exactly with what's quoted in a given post.

## What's covered beyond the three articles (corner-scenario enrichment)

- **Refined Specification API** (`AuthorSpecifications.java`): `PredicateSpecification` reused across a read and a bulk delete, an explicit `DeleteSpecification` (`CriteriaDelete`-backed), and an `UpdateSpecification` (`CriteriaUpdate`-backed bulk update composed from an `UpdateOperation` + a `where(...)` predicate).
- **`JpaSort.unsafe(...)` with a `CASE` expression** - a real `ORDER BY case when country = 'US' then 0 else 1 end` sort combined with a plain derived query.
- **`Money`, an `@Embeddable` record value object** on `Book.price`, with derived queries that traverse the embedded path (`findByPriceAmountGreaterThanEqual`, `findByPriceAmount`).
- **A genuine corner case, found by actually running it**: a derived-query class-based (record) projection resolves constructor-parameter names against *direct* entity properties only. `BookSummary(String title, BigDecimal amount)` does **not** resolve `amount` against the nested `price.amount` path via a plain `findBy...` derived method - it throws `PropertyReferenceException: No property 'amount' found for type 'Book'`. The fix is an explicit `@Query` constructor expression (`select new ...BookSummary(b.title, b.price.amount) from Book b where ...`), which does work for nested/embedded paths. See `BookRepository.findByPriceAmountLessThanEqual`.

All of the above is exercised by both the demo runner (`DemoRunner.java`, sections H-L) and dedicated tests in `MigrationBehaviorTests.java`.