How to override correctly equals/hashCode for jpa entity

Configuration

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

Solutions

Equals by all fields, hashCode by default

see: /src/test/java/hello/entity/defaultHashCode/GoodTest.java

Natural id, equals by all fields, hashCode by only natural id

see: /src/test/java/hello/entity/naturalId/BookTest.java

Equals by all fields, hashCode by surrogate id

see: /src/test/java/hello/entity/overrideAllFields/UserTest.java

Equals by all fields, hashCode - constant

see: /src/test/java/hello/entity/overrideAllFields_hashCodeConstant/ClientTest.java

Conclusion

• If your entity has a business key or a natural ID, you can use it within your equals() and hashCode() method.
• If you set your primary key values programmatically, you can use its value in your equals check and when you calculate the hash code.
• If you tell Hibernate to generate your primary key values, you need to use a fixed hash code, and your equals() method requires explicit handling of null values.