qiangzhu / uuid-jpa-rest-example

Example of using UUIDs as primary keys in EclipseLink / Spring-Data REST

JPA UUID primary key example

Example project for demonstrating the use of UUIDs as primary keys in JPA and Spring Data REST. Current master branch uses hibernate as implementation, while the eclipselink tag shows an alternative implementation using EclipseLink as JPA provider.

Special Features

UUID as primary key

This service is using UUIDs as primary keys. The UUID is not naïvely persisted into the DB as CHAR(36), but shifted into a BYTE(16) structure.

It is using the Java Uuid Generator library for generating Version-1 UUIDs, still hiding the actual implementation behind a functional interface ( UUIDGenerator ).

Business vs. technical identifiers

In addition to the id, which is immutable, there is the name property as business identifier of a resource. Most business identifiers in the wild are not immutable, unfortunately. Still, by default the URI is composed using the business identifier, creating human-readable URIs. For the case of "renamed mice", there is still the possibility of a look-up via the finder resource /search/findById.

JPA auditing and optimistic locking

The Mouse entity has support for last-modified-based and ETag-based optimistic locking. The extra properties ( optLock, createdAt, lastModifiedAt ) are hidden from the business model and resource representations (i.e. private fields without getters/setters)

EclipseLink load-time weaving

Although not directly related to UUID persistence, this project also applies EclipseLink's load-time weaving, but only when spring-instrument.jar is present on the classpath. (see the eclipselink tag)

How to run

On the command-line run ./gradlew bootRun and open a browser at http://localhost:8080/.

Further references:

• https://en.wikipedia.org/wiki/Universally_unique_identifier
• https://github.com/cowtowncoder/java-uuid-generator
• http://mysql.rjweb.org/doc.php/uuid
• http://mysqlserverteam.com/storing-uuid-values-in-mysql-tables/
• https://www.clever-cloud.com/blog/engineering/2015/05/20/why-auto-increment-is-a-terrible-idea/