Hello,
There is a problem in the SPIN API with printing an ORDER BY expression that
contains a query variable.
Let's say I have the following SPIN description of a SPARQL query with an
ORDER BY clause:
_:myQuery
rdf:type sp:Select ;
# ...
sp:orderBy ( [sp:varName "dep"^^xsd:string] ) .
When I print this query with the SPIN API using the class 'StringPrintContext'
I would expect to get something like:
SELECT ... {
...
}
ORDER BY ?dep
but what I get is
SELECT ... {
...
}
ORDER BY (sp:Variable())
I tried to track this problem down. It seems to be in the method
'printOrderByExpression' of class 'QueryImpl'. This method is called with a
Resource which is of rdf:type sp:Variable and it represents the variable. The
first thing 'printOrderByExpression' with this Resource, it tries to cast it to
a 'FunctionCall' which works. Therefore, it tries to print the variable as if
it were a 'FunctionCall'.
I think this problem can be fixed by trying to cast the Resource to a
'Variable' before casting it to a 'FunctionCall' and if it turns out to be a a
variable (i.e. if the cast works) then use the functionality to print
variables.
Greetings,
Olaf
----------------------
Olaf Hartig (http://olafhartig.de)
Database and Information Systems Research Group
Department of Computer Science
Humboldt-Universität zu Berlin
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