How to Implement hashCode() and equals() for JPA Entities Without Breaking Identity?

The JPA hashCode() / equals() Dilemma: A JPA-Neutral Perspective

Implementing hashCode() and equals() for JPA entities can present several challenges, particularly regarding conformancy to contract and identity detection. Discussing the issue from a JPA-implementation-neutral standpoint (specifically with EclipseLink in mind), this article explores the available options and their implications.

Possible Implementations with Trade-offs

1. Object.hashCode() and Object.equals(): This default implementation ensures contract conformity but fails to identify identical objects and may cause issues with detached entities.
2. hashCode()/equals() by Primary Key: Adheres to the hashCode()/equals() contract but breaks identity for detached entities due to transient primary key values.
3. hashCode()/equals() by Business-Id: Provides correct identity but may still break the contract and cause issues with foreign keys.

Question and Recommendations

Question 1: Have any options or trade-offs been overlooked?

Answer: The article referenced, "Don't Let Hibernate Steal Your Identity," suggests that assigning object IDs during instantiation simplifies object identity and reduces code complexity.

Question 2: Which option is recommended?

Answer: The solution suggested in the article recommends assigning object IDs at instantiation, rather than relying on JPA implementations. This approach ensures consistency and simplifies identity management.

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