Feature/sparql fed query #1134
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Feature/sparql fed query #1134
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dpetran
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This is much more inefficient, but some remote services can't handle a VALUES clause with variables that aren't in the query. We'll need to adding SERVICE var filtering in the future anyways to account for $-prefixed vars in the SERVICE clause, but this is the simple and correct way to handle it for now.
onto-chan! closes the channel after it is done putting its collection, and I think it looks better than calling >! and the close! in a do-block. Without closing the downstream consumers are blocked.
These will be a useful performance enhancement, but aren't needed for this first iteration. The only additional validation they require is to only bind vars that are present in the SERVICE clause - I ran into some errors from 3rd party services when trying to handle vars not in the clause (though that is not strictly in spec for SPARQL).
We can't test responsive endpoints within this repo, so we'll just verify that errors are handled correctly.
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https://github.com/fluree/core/issues/207
Introduces support for the SPARQL
SERVICEclause: https://www.w3.org/TR/sparql11-federated-query/#serviceThe approach here is a very naive one, but it is in compliance with the spec. There are many performance improvements we can use to make this faster if the current implementation is not sufficiently fast for a given use.
SPARQL is translated into jld-query syntax but the
SERVICEclause is retained as a raw string. This raw SPARQL string is turned into a valid SPARQL query by prepending it with aWHEREand prepending that with any defined prefixes from the json-ld@contextand and aSELECT *clause. This is then sent to the specified SPARQL service endpoint and the JSON results are parsed and turned into solutions.It is not possible to test a working SPARQL service endpoint within this repo, so the tests are incomplete. However, Fluree Server does implement a valid SPARQL endpoint and it is entirely valid for a query to reference its own hosting service, so there are more complete tests in fluree/server#186.