Dear all,
We are having a little problem with left-empty optional queries, which I
believe might be a little bug in how rdflib is dealing with query results with
empty bindings.
Consider an EMPTY graph and execute the following query
ASK { OPTIONAL {?x ?y ?z} }
It yields true, as other SPARQL engines. However, the query
SELECT * { OPTIONAL {?x ?y ?z} }
while yielding a SPARQLResult with one binding (len=1), its generator yields no
ResultRow. Other engines return a single row, with all the projected variables
set to None.
Is this the correct behaviour? If not, I believe the problem is in file
rdflib/query.py
in the code
if self._genbindings:
for b in self._genbindings:
if b: # don't add a result row in case of empty binding {}
self._bindings.append(b)
yield ResultRow(b, self.vars)
self._genbindings = None
else:
for b in self._bindings:
if b: # don't add a result row in case of empty binding {}
yield ResultRow(b, self.vars)
Both `if b:`are blocking the empty binding to appear in the result.
Some more discussion on this topic can be found in:
https://stackoverflow.com/questions/25131365/sparql-optional-query
at the end of the first answer.
best regards and thanks for the this great tool,
Sandro R. Fiorini
--
http://github.com/RDFLib
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