sdjpa4-demo/README.md

sdjpa4-demo

Runnable companion project for the Spring Data JPA 3 to 4 migration series on ankurm.com:

• Spring Data JPA 3 to 4 Migration Guide (overview, start here)
• Migration Baseline
• Query Engine Rewrite: Criteria to JPQL
• Advanced Migration: Specifications, AOT, EntityManager

Four entities, three repositories, a @NullMarked package, 20 passing behavior tests, and an A-L demo runner that prints every labelled console output shown in the articles. Boots H2 in memory, so there's nothing to install beyond a JDK.

Built and verified on Eclipse Temurin JDK 21, Spring Boot 4.0.6, Spring Data JPA 4.0.6, Hibernate ORM 7.2, H2 in-memory.

Run it

git clone https://ankurm.com/git.app/asmhatre/sdjpa4-demo.git
cd sdjpa4-demo
./mvnw spring-boot:run   # prints the labelled A-L demonstrations
./mvnw test               # runs the 20 behavior tests (all green)

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.