Learn Hibernate @OneToOne

Configuration

For main and test dirs: cp application.properties.dist application.properties

/src/main/java/hello/entity/bidirectional/mappedBy

Where User is owner of relations.

It is important to understand that the relationship is created only when set Role to User and save User.

/src/main/java/hello/entity/bidirectional/twoMain

Where Book and Author is owners of relations.