Another thing to keep in mind is that IF will return nothing if the
condition is returning "unbound" (fail). For example,
IF(strlen(?a) > 0, "1", "2")
will return nothing if ?a is not a string - it will fail and return
unbound - not "2". A safer way of expressing this would be
IF(bound(?a) && strlen(?a) > 0, "1", "2")
For some use cases, the COALESCE keyword is a better option than IF.
Not sure if this is on topic for your specific scenario.
Holger
On 2/10/2015 6:16, Jack Hodges wrote:
I was testing a simple conditional in SPARQL and it wasn't working. So
I went to the documentation and wrote the test conditional and it
worked, but do not understand why mine isn't working. The test
conditional compares 2 integers and displays 2 strings. I augmented
that test to have another nested IF and it still works.
My query is based on a BIND of 2 expressions to strings. Here is what
it looks like:
SELECT ?res
WHERE {
BIND ("foo" AS ?f) .
BIND ("bar" AS ?b) .
BIND ((IF(?f, ?f, IF(?b, ?b, "NA"))) AS ?res) .
}
This returns "foo". If I remove the first BIND statement there is no
result. I tried changing this test to:
SELECT ?res
WHERE {
BIND ("foo" AS ?f) .
BIND ("bar" AS ?b) .
BIND ((IF(fn:string-length(?f) > 0, ?f, IF(fn:string-length(?b) >
0, ?b, "NA"))) AS ?res) .
}
and it returns "foo". If I change the first size to 3, then it returns
"bar". If I change the second size to 3 it returns "NA".
But in 'my' query this doesn't work. Here is the query:
SELECT DISTINCT *
WHERE {
BIND
(act:commonSubclassLabel("http://developer.runkeeper.com/healthgraph#Spinning";)
AS ?res1) .
BIND
(act:commonSuperclassLabel("http://developer.runkeeper.com/healthgraph#Spinning";)
AS ?res2) .
BIND ((IF(fn:string-length(?res2) > 0,
?res2, IF(fn:string-length(?res1) > 0, ?res1, "NA"))) AS ?res) .
}
The function calls to 'commonSubclassLabel' and
'commonSuperclassLabel" work fine on their own (both return strings),
and the result returned is ?res2 if its length exceeds 0. If not,
there is a value for ?res1 but it doesn't ever get bound to ?res. If I
swap ?res2 and ?res1 in the last BIND the same query works for ?res1
but not ?res2, so there is something in my IF statements 'THEN' block
that doesn't work. If I replace the THEN block with just ?res1 (or
?res2 as the case may be), nothing changes in the result.
As you can see, I have worked myself into a lather over this by making
it more complex than it should have to be, but as is normal in such
cases when the simple logic didn't work I began more and more
convoluted things.
Any pointers would be greatly appreciated!
These queries are being executed in TBCME v4.2.
Jack
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