Java persistence with JPA and Hibernate: Entities and relationships
The Jakarta Persistence API (JPA) is a Java specification that bridges the gap between relational databases and object-oriented programming. This two-part tutorial introduces JPA and explains how Java objects are modeled as JPA entities, how entity relationships are defined, and how to use JPA's EntityManager with the Repository pattern in your Java applications. This gives you all the basics for saving and loading application state.
Note that this tutorial uses Hibernate as the JPA provider. Most concepts can be extended to other Java persistence frameworks.