Class: SparqlAdapter

Inherits:
ActiveRdfAdapter
  • Object
show all
Defined in:
lib/activerdf_sparql/sparql.rb

Overview

SPARQL adapter

Instance Method Summary collapse

Constructor Details

#initialize(params = {}) ⇒ SparqlAdapter

Instantiate the connection with the SPARQL Endpoint. available parameters:

Raises:

  • (ActiveRdfError) 


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# File 'lib/activerdf_sparql/sparql.rb', line 17

def initialize(params = {})	
	@reads = true
	@writes = false

	@url = params[:url] || ''
	@result_format = params[:results] || :json
	
	known_formats = [:xml, :json, :sparql_xml]
	raise ActiveRdfError, "Result format unsupported" unless 
	known_formats.include?(@result_format)
	
	$activerdflog.info "Sparql adapter initialised #{inspect}"
end

Instance Method Details

#execute_sparql_query(qs, header, &block) ⇒ Object

do the real work of executing the sparql query



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# File 'lib/activerdf_sparql/sparql.rb', line 46

def execute_sparql_query(qs, header, &block)
	$activerdflog.debug "executing query #{qs} on url #@url"

	# encoding query string in URL
	url = "#@url?query=#{CGI.escape(qs)}"

   # querying sparql endpoint
	response = ''
	begin 
	  open(url, header) do |f|
			response = f.read
		end
	rescue OpenURI::HTTPError => e
		raise ActiveRdfError, "could not query SPARQL endpoint, server said: #{e}"
		return []
	rescue Errno::ECONNREFUSED
		raise ActiveRdfError, "connection refused on SPARQL endpoint #@url"
		return []
 	end

   # we parse content depending on the result format
   results = case @result_format
					 	when :json 
							parse_json(response)
					 	when :xml, :sparql_xml
						 	parse_xml(response)
					 	end

   if block_given?
     results.each do |*clauses|
       yield(*clauses)
     end
   else
     results
   end
end

#query(query, &block) ⇒ Object

query datastore with query string (SPARQL), returns array with query results may be called with a block



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# File 'lib/activerdf_sparql/sparql.rb', line 37

def query(query, &block)
	time = Time.now
   qs = Query2SPARQL.translate(query)
	$activerdflog.debug "executing sparql query #{query}"

	execute_sparql_query(qs, header(query), &block)
end

#size ⇒ Object 



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# File 'lib/activerdf_sparql/sparql.rb', line 31

def size
	query(Query.new.select(:s,:p,:o).where(:s,:p,:o)).size
end