sparql/client

query = SPARQL::Client::Query

if I have this
query = query.select.prefix("fb <http://rdf.freebase.com/ns/>").prefix("dc:
<http://purl.org/dc/elements/1.1/")

how do I use the prefixes in a where clause?

query = query.select(:costar, :fn)
query = query.where([:s,:p,:o]) works

but
query = query.where([:s, fb:film.film.performances, :pl]) doesn't

gives a expecting tASSOC error

thanks in advance