How should equals and hashcode be implemented when using JPA and Hibernate

by

Hibernate has a nice and long description of when / how to override equals() / hashCode() in documentation

The gist of it is you only need to worry about it if your entity will be part of a Set or if you’re going to be detaching / attaching its instances. The latter is not that common. The former is usually best handled via:

  1. Basing equals() / hashCode() on a business key – e.g. a unique combination of attributes that is not going to change during object (or, at least, session) lifetime.
  2. If the above is impossible, base equals() / hashCode() on primary key IF it’s set and object identity / System.identityHashCode() otherwise. The important part here is that you need to reload your Set after new entity has been added to it and persisted; otherwise you may end up with strange behavior (ultimately resulting in errors and / or data corruption) because your entity may be allocated to a bucket not matching its current hashCode().

More Related Contents:

  1. Apache Commons equals/hashCode builder [closed]
  2. How to fix the Hibernate “object references an unsaved transient instance – save the transient instance before flushing” error
  3. Hibernate Annotations – Which is better, field or property access?
  4. How to map calculated properties with JPA and Hibernate
  5. Understanding the workings of equals and hashCode in a HashMap
  6. How to print a query string with parameter values when using Hibernate
  7. When and why JPA entities should implement the Serializable interface?
  8. I found JPA, or alike, don’t encourage DAO pattern
  9. Hibernate – @ElementCollection – Strange delete/insert behavior
  10. session.connection() deprecated on Hibernate?
  11. Location of hibernate.cfg.xml in project?
  12. Why should I override hashCode() when I override equals() method?
  13. how to configure hibernate config file for sql server
  14. How to set a default entity property value with Hibernate
  15. Should I write equals() and hashCode() methods in JPA entities?
  16. mappedBy reference an unknown target entity property
  17. Hibernate use of PostgreSQL sequence does not affect sequence table
  18. Primitive or wrapper for hibernate primary keys
  19. How to use Hibernate @Any-related annotations?
  20. How default .equals and .hashCode will work for my classes?
  21. Create the perfect JPA entity [closed]
  22. How to turn off hbm2ddl?
  23. Hibernate triggering constraint violations using orphanRemoval
  24. HibernateException: Couldn’t obtain transaction-synchronized Session for current thread
  25. Unable to create requested service [org.hibernate.engine.jdbc.env.spi.JdbcEnvironment]
  26. Change Table Name of an Entity on runtime? [duplicate]
  27. Hibernate saving User model to Postgres
  28. How to map one class to different tables using hibernate/jpa annotations
  29. Java: Use hashCode() inside of equals() for convenience?
  30. How to use JTA support in Tomcat 6 for Hibernate?

Leave a Comment