error method missing when enumerate solution query

[scauglog]

Sometimes when i ran a query and enumerate the solution an error occur

C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/rdf-1.0.6/lib/rdf/query/solution.rb:257:in 'method_missing': undefined method 'image_url' for #<RDF::Query::Solution:0x2b0b8b8> (NoMethodError)

It's very strange because i can rerun the same query, without any change, few minute later and this message doesn't show up.

this is the query i run :

a=[]
@repo.build_query do |q|
q << [item_uri,SCHEMA.associatedMedia,:uri]
q << [:uri,SCHEMA.image, :image_url]
end.run do |s|
a << s.image_url.to_s
end


[cagdasolgun]

i think the correct syntax is like

a=[]
@repo.build_query do |q|
q.pattern [item_uri,SCHEMA.associatedMedia,:uri]
q.pattern [:uri,SCHEMA.image, :image_url]
end.run do |s|
a << s.image_url.to_s
end

And maybe you can print out solutions after you run query.

end.run do |s|
puts s.inspect
end

Also you can check query patterns to see if your statements are correct.

query = @repo.build_query do |q|
q.pattern [item_uri,SCHEMA.associatedMedia,:uri]
q.pattern [:uri,SCHEMA.image, :image_url]
end

puts query.patterns.inspect

[scauglog]

thanks for the answer but rewrite the query with pattern didn't solve my problem. I have write a sparql query and this seems better.

a=[]
@repo.sparql_query("SELECT ?image_url WHERE {
  <#{item_uri}> <#{SCHEMA.associatedMedia}> ?uri.
  ?uri <#{SCHEMA.image}> ?image_url.}"
).each do |s|
  a << s.image_url.to_s
end

[cagdasolgun]

quick fix about example;

run method returns an enumeration. And it should be ,

a=[]
@repo.build_query do |q|
q.pattern [item_uri,SCHEMA.associatedMedia,:uri]
q.pattern [:uri,SCHEMA.image, :image_url]
end.run.each do |s|
a << s.image_url.to_s
end