Semantics of `Resource::isMemento`

[ajs6f]

Under what circumstances is Resource::isMemento meant to return true? In particular, should all calls to CassandraResourceService.get(IRI, Instant) return Resources whose isMemento methods return true?

[acoburn]

This depends a bit on the implementation. If the persistence backend supports versioning, then yes, a response to ResourceService.get(IRI, Instant) would return a Resource to which the isMemento would return true. But if the persistence layer does not support versioning, then you may just return an ordinary Resource to which the isMemento method returns false.

[ajs6f]

It's coming up for me because I am about to embark on impling versioning. So in a versioning backend, the isMemento on Resources that were returned from (plain) ResourceService.get(IRI) should return false (every time) but the isMemento on Resources that were returned from (fancy) ResourceService.get(IRI, Instant) should always return true, right?

[acoburn]

That is correct. You can see that the default implementation for this method returns false: https://github.com/trellis-ldp/trellis/blob/master/trellis-api/src/main/java/org/trellisldp/api/Resource.java#L150, so there's no need to do anything special for the ordinary resources.

[ajs6f]

Cool, I will send a PR with more Javadocs.