Value types in JPA

[nlisker]

Value Objects have been integrated into Java 28 in preview mode. Is there any bearing on JPA with regard to value objects that needs to be documented or implemented in the future? A lot of the Basic types will be converted to value objects.

For example, if I declare

value class Pages {

    private long pages;  // implicitly final
}

will there be any difference with respect to the same class without the value declaration?

It will be some time before value types leave preview, but it's good to have some foresight for JPA/JakartaEE because their releases are less frequent than Java's.

[AleksNo]

I guess, value objects will have the same limitations like records. Value objects are immutable and they are out as entities.

[nlisker]

The question is not about having value types as entities, which as you pointed out, is conflicting with mutability. The question is about using them as fields in an entity.

[beikov]

Since value classes don't have identity and are immutable, they could at most be used as embeddable types. I don't think we have to clarify anything in the Jakarta Persistence specification for that to work.

[gavinking]

I guess, value objects will have the same limitations like records.

Need to check the spec to see whether they are literally considered a type of record. If they aren't, then we should at least clarify whether a provider is required to support them where record are allowed; if the are, then my kneejerk reaction is that there's probably not much to do.

[nlisker]

I guess, value objects will have the same limitations like records.

Need to check the spec to see whether they are literally considered a type of record. If they aren't, then we should at least clarify whether a provider is required to support them where record are allowed; if the are, then my kneejerk reaction is that there's probably not much to do.

Value objects are not necessarily records, they can be ordinary classes. Because both impose shallow immutability, many records will be value types. The primitive wrappers will also be converted to value types, so will other JPA Basic types like LocalDate, LocalTime, and LocalDateTime, none of which are records.

[gavinking]

@nlisker In that case we should definitely state that value types can't be entities, but they can be embeddable types (just like records).

[gavinking]

Please review #1165.