Slowly Changing Dimension (SCD) Example

This example shows using a very simplistic SCD Type 2 persistence using JPA. This demonstrates:

• Typical 'Person' entity:
  • By name,
  • By name at a point-in-time (instant),
  • Audit trail,
  • All latest vales,
  • All audit trail (rarely used, but useful example non-the-less),
• Time-series:
  • Raw,
  • Tumbling windows with variable alignment period and start and end dates using either date or date and time.

ℹ️ For simplicity sake, this doesn't use start/end dates, it just uses a inserted value as part of the key.

ℹ️ Returned time-series data windows are [start, end) meaning start is inclusive and end is exclusive as this tends to look cleaner.

Notes:

• It seems EclipseLink refuses to compile with Java 16. It's due to a really old version of ASM and that's not going to be updated until 3.0.1 (aka Jakarta). Workaround is to use bump to just org.eclipse.persistence:org.eclipse.persistence.asm:3.0.1.
• Regardless of what H2 documentation states, it doesn't work with java.time.Instant (or it could be PIBCAK!). So I had to create a attribute converter to do this,
• E-Tag is generated from the hashcode of the key of an entity. For a collection of entities it gets all the keys and creates it from them. The potential for collision is probably not wonderful, but for the purposes of this it's adequate',
• If you want to view your data, go to localhost:8082 and use JDBC URL jdbc:h2:mem:app,
• Some of the queries use correlated subqueries, which can be a concern but this can be mitigated with indexes on the correlation criteria and some DBs can rewrite them.

To run pgAdmin:

docker run -p 8082:80 `
	-e '[email protected]' `
	-e 'PGADMIN_DEFAULT_PASSWORD=pwd' `
	--rm `
	-d `
	dpage/pgadmin4

When the application is running locally you can then connect to your database using: host.docker.internal:<port>