ResourceSupport might benefit from having a method that returns a list of links that have the same rel.

[vivin]

Currently there is a method called getLink(String rel) that returns a link with the given rel. However, it is possible to have multiple links that share the same rel. Therefore, I think it might be beneficial to have a method like so:

public List<Link> getLinks(String rel);

Which will return a list of links that have the given rel.

[chrylis]

#157

[vivin]

Ahh thanks! I did not see the original issue. @olivergierke thoughts about this?

[chrylis]

That's not a 100% duplicate, but I think we're looking at the same issue. Essentially, the current getLink (1) returns a single value and (2) doesn't play nicely with the map-navigation syntax offered by Groovy and *EL. What I'd prefer to see in place of your signature is

Map<String, Collection<Link>> getLinks();

That way, something like myobj.links['picture'].href would work.

[vivin]

I think changing the signature of the existing one would be a breaking change, unfortunately. The new method I suggested would sort of do what you want, except instead of working with a map directly, you're asking the ResourceSupport class to filter out links with the rel you want. The performance would be lacking since it would be O(n) since you have to traverse the entire list. I think that could be mitigated if the internal representation is modified from List<T> into Map<K, V>.

[chrylis]

It absolutely would be a breaking change, but we're still at major version 0. (I note additionally that HAL seems to specify that link rels are unique per entity, which means that the current list-based implementation is also problematic in permitting duplicates.) Changing the internal representation is what I recommended a while back, but I haven't heard any comments.

[dschulten]

Hi,

although I find it problematic, too, to use duplicates, HAL specifically
allows them in section 4.1.1 where it says that the value of the rel may be
an array of link objects. It uses this feature explicitly for curies.

Best,
Dietrich

Am 23. März 2015 04:24:11 schrieb Christopher Smith notifications@github.com:

It absolutely would be a breaking change, but we're still at major version
0. (I note additionally that HAL seems to specify that link rels are unique
per entity, which means that the current list-based implementation is also
problematic in permitting duplicates.) Changing the internal representation
is what I recommended a while back, but I haven't heard any comments.

---

Reply to this email directly or view it on GitHub:
#318 (comment)

[chrylis]

Aha. Well, in that case, something with the semantics of a multimap are probably best.

[vivin]

Yes, a rel can represent multiple links and HAL does allow that. Internally a Map<String, List<Link>> would make much more sense, I think, but I haven't heard any comments either about this issue (and some others as well).

[odrotbohm]

What if we just added List<Link> getLinks(String rel)?

[chrylis]

That would be an improvement, but it's still awkward in contexts (Groovy, SpEL) that support map-style syntax.

[odrotbohm]

foo.getLinks(…).href?

[chrylis]

Works okay if you're looking for links for a specific rel (though still more cumbersome than foo.links.picture[0].href, since getLinks isn't a property accessor), but there's no simple way to iterate over rels.