| Re: [lyo-dev] Keep Uses order |
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Guillaume,
Let me clarify a bit more as I dug up some notes. There are three places where ordering can be considered as far as OSLC Servers are concerned:
1) Usual GET/PUT OSLC requests (raw RDF inside the body).
2) OSLC Query results.
3) SPARQL results.
§1 Raw RDF does not have ordering guarantees on properties. Links:
"Information is represented by a set of RDF triples, often called a model. As it is a set, there is no ordering"
§2 The only place where we break RDF convention is the OSLC Query results, where the order of the returned results matters. The actual
spec says in [query-50] that ordered resources should come in the right order. However, it has been proposed to change
that to express ordering explicitly but the current spec allows [query-51] to satisfy this. Jim may have a different viewpoint on this.
§3 SPARQL results return ordered set of rows. However, we don't expect SPARQL to be used anywhere by default and don't have special code to handle it.
Having said that, in the newly generated code (not used by default in Lyo yet) we use Sets and HashSets: https://github.com/eclipse/lyo.domains/blob/master/oslc-domains/src/main/java/org/eclipse/lyo/oslc/domains/rm/RequirementCollection.java
Ideally, I would like to generate methods like
Set<IResource> getSomeProperty();
void setSomeProperty(Collection<IResource> resources);
But this would require an incompatible change to the API and we don't want to break compatibility for little or no reason.
Bottom line: if you want to iterate the items of a Set in some order, better use a custom Comparator when creating a List copy of the Set:
https://stackoverflow.com/a/45696217
-- /Andrew
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