JPA links (updated)

Reference implementation.

Official documentation:

• JSR 317 JPA 2 specification
• JSR 338 JPA 2.1 specification
• API Javadoc
• Hibernate API Javadoc

Others:

•  Wikibook (incomplete)

Providers often have good JPA documentation as well. Might include extensions (and JDO stuff) though:

• Open JPA
  
• EclipseLink JPA
• DataNucleus
• ObjectDB

Specific topics:

• JPA 2.x what's new
• Where to define JPQL queries
• Caching 
• Validation

Background:

•  ORM hate