Accomodate domain object identity in @EqualsAndHashCode

[projectlombok]

Accomodate domain object identity in @EqualsAndHashCode

[lombokissues]

👤 lhoriman   🕗 Aug 18, 2009 at 01:34 UTC

For JPA domain objects (classes annotated with @ Entity), equality is best defined as:

• Are the classes equal
• Are the ids equal

The id of a JPA entity will either be:

• A compound of all the fields annotated with @ javax.persistence.Id
  or:
• The single field annotated with @ javax.persistence.EmbeddedId

Some things to consider:

• @ Id and @ EmbeddedId annotations might come from superclasses.
• It might also be a good idea to have the @ EqualsAndHashCode(include={"xxx"}) option as well
  since it's still possible for (masochistic) developers to define the ids and relationships in XML.
  And it's a useful construct in general.
• You might want this to only apply to @ Entity objects.

[lombokissues]

👤 reinierz   🕗 Aug 18, 2009 at 12:07 UTC

This is going to be rather complicated. Full discussion is here:

http://groups.google.com/group/project-lombok/browse_thread/thread/b0e6a34d1bc72526

[lombokissues]

👤 reinierz   🕗 Sep 01, 2009 at 23:45 UTC

We'll support it via include, as triggering on @ Id/@ EmbeddedId has far too many complications (see previous
link).

[lombokissues]

👤 jnorris10   🕗 Sep 02, 2009 at 16:02 UTC

Defaulting JPA entities to base their equality on @ Id/@ EmbeddedId does not seem like a good idea. Entities
often have a "natural" identifier which is separate from @ Id. In this case, @ Id is used as a surrogate key (making
it easier to manage ORM mapping and refactor the DB schema later). Another advantage is it lets the natural
constraints be enforced in the domain model independent of the persistence mechanism used. Also, in cases
where @ Id is generated from the DB, it allows objects to have a valid notion of equality before they are persisted.

I agree with reinierz, an explicit include properties mechanism is best here. It's the most clear and simple.

[lombokissues]

👤 lhoriman   🕗 Sep 02, 2009 at 16:07 UTC

I think everyones on the same page - an "include" member of the @ EqualsAndHashCode annotation would be
great.

[lombokissues]

👤 reinierz   🕗 Sep 02, 2009 at 23:47 UTC

addressed in f1124aa which will be rolled out in v0.8.5. The
'includes' parameter is called 'of', so you could do:

@ EqualsAndHashCode(of="id")
@ Entity
public class SomePersistedClass { ... }

We've also added fields that start with $ as default excludes. Lombok's own @ Synchronized can generate
these fields, and I expect other automated tools will as well. $ is understood to mean 'generated', and it
seems safer to exclude them by default.

[lombokissues]

End of migration