I have a SPARQL CONSTRUCT that works like this:
CONSTRUCT {
?uri rdfs:label ?label;
foo:has-value ?v.
}
WHERE {
?uri
rdfs:label ?label;
foo:has-flag ?f.
BIND ( IF ( ?f = 0, "Value for Zero", IF ( ?f = 1, "Value for One", '' ) ) AS ?v )
}
The problem is that when ?f
is neither 0 nor 1 (but still has some value) I don't want the has-value
statement at all. With the syntax above, I get ?uri has-value ''
. It would work, if I could assign some sort of "null" to ?v
, or avoid the binding, but I cannot find anything like that in the specs.
Any solution?
EDIT : The solution by Scott works for common graph-based queries. The case I came from involves the use of VALUES, is more complicated and I couldn't find a solution so far.
EDIT/2 : the error-triggering solution , suggested by Andy in the Jena mailing list, works fine! Another approach, which I find more readable, is binding an unbound variable when we want to skip the original value.
Given feedback in the comments, here is a solution based on OPTIONAL
that should meet all of the criteria:
CONSTRUCT {
?uri rdfs:label ?label;
foo:has-value ?v.
}
WHERE {
?uri rdfs:label ?label .
?uri foo:has-flag ?f.
OPTIONAL { FILTER (?f = 0)
BIND("Value for Zero" AS ?v)
}
OPTIONAL { FILTER (?f = 1)
BIND("Value for One" AS ?v)
}
}
As pointed out, this previous solution will not cover the case where there is label, but ?f
is not 0 or 1:
CONSTRUCT {
?uri rdfs:label ?label;
foo:has-value ?v.
}
WHERE {
?uri
rdfs:label ?label;
foo:has-flag ?f.
FILTER (?f = 0 || ?f = 1)
BIND ( IF ( ?f = 0, "Value for Zero", IF ( ?f = 1, "Value for One", '' ) ) AS ?v )
}
A bit hacky but should work with creating a blank node and then filter out those:
CONSTRUCT {
?uri rdfs:label ?label;
foo:has-value ?v.
}
WHERE {
?uri rdfs:label ?label .
OPTIONAL {
?uri foo:has-flag ?f.
BIND ( IF ( ?f = 0, "Value for Zero",
IF ( ?f = 1, "Value for One", BNODE() )
) AS ?v )
FILTER(!ISBLANK(?v))
}
}
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