Java persistence resources:
https://docs.oracle.com/javaee/7/tutorial/partpersist.htm (overall Oracle documentation index)
https://docs.oracle.com/javaee/7/tutorial/persistence-intro001.htm (cap 37 of Oracle documentation)
https://docs.oracle.com/javaee/7/tutorial/persistence-basicexamples001.htm#GIQST (cap 38 of Oracle documentation)
https://nikojava.wordpress.com/2011/08/04/essential-jpa-relationships/ Good on relationships
http://www.jpab.org/All/All/All.html Some performance comparison
Miscellaneous resources:
https://www.tutorialspoint.com/jpa/index.htm
https://docs.oracle.com/cd/E19798-01/821-1841/gjiwz/index.html (embeddable classes)
Example of JPA from a standalone program (Java SE) in Netbeans
Tutorial on ORM CRUD operations through RESTful endpoints in Spring
Another tutorial on ORM CRUD operations through RESTful endpoints in Spring
Documentation of the JPARepository class
Presentations:
Code samples: