Class: FederationManager

Inherits:
Object
  • Object
show all
Defined in:
lib/active_rdf/federation/federation_manager.rb

Overview

Manages the federation of datasources: distributes queries to right datasources and merges their results

Class Method Summary collapse

Class Method Details

.add(s, p, o, c = nil) ⇒ Object

add triple s,p,o (context is optional) to the currently selected write-adapter



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# File 'lib/active_rdf/federation/federation_manager.rb', line 10

def FederationManager.add(s,p,o,c=nil)
  benchmark("SPARQL/RDF", Logger::DEBUG) do |bench_message|
    bench_message << "ADD #{s} - #{p} - #{o} : #{c}" if(bench_message)
    # TODO: allow addition of full graphs
    raise ActiveRdfError, "cannot write without a write-adapter" unless ConnectionPool.write_adapter
    ConnectionPool.write_adapter.add(s,p,o,c)
  end
end

.clear(context = nil) ⇒ Object

Clear the store (or the given context)

Raises:

  • (RuntimeError) 


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# File 'lib/active_rdf/federation/federation_manager.rb', line 38

def FederationManager.clear(context=nil)
  # FIXME: Make sure that all adapters support clearing
  raise(RuntimeError, "Adapter #{ConnectionPool.write_adapter.class} doesn't support clear") unless(ConnectionPool.write_adapter.respond_to?(:clear))
  ConnectionPool.write_adapter.clear(context)
end

.delete(s, p, o, c = nil) ⇒ Object

delete triple s,p,o (context is optional) to the currently selected write-adapter



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# File 'lib/active_rdf/federation/federation_manager.rb', line 20

def FederationManager.delete(s,p,o,c=nil)
  benchmark("SPARQL/RDF", Logger::DEBUG) do |bench_message|
    bench_message << "DELETE #{s} - #{p} - #{o} : #{c}" if(bench_message)
    raise ActiveRdfError, "cannot write without a write-adapter" unless ConnectionPool.write_adapter
    # transform wildcard symbols to nil (for the adaptors)
    s = nil if s.is_a? Symbol
    p = nil if p.is_a? Symbol
    o = nil if o.is_a? Symbol
    ConnectionPool.write_adapter.delete(s,p,o,c)
  end
end

.delete_all(resource) ⇒ Object

delete every triples about a specified resource



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# File 'lib/active_rdf/federation/federation_manager.rb', line 33

def FederationManager.delete_all(resource)
  delete(resource, nil, nil)
end

.query(q, options = {:flatten => true, :result_format => nil}) ⇒ Object

executes read-only queries by distributing query over complete read-pool and aggregating the results



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# File 'lib/active_rdf/federation/federation_manager.rb', line 47

def FederationManager.query(q, options={:flatten => true, :result_format => nil})
  if ConnectionPool.read_adapters.empty?
    raise ActiveRdfError, "cannot execute query without data sources" 
  end

  benchmark("SPARQL/RDF", Logger::DEBUG) do |bench_message|
    # Only build the benchmark message if we need it
    bench_message << ((q.class == String) ? q : q.to_sp) if(bench_message)
    # ask each adapter for query results
    # and yield them consequtively
    if block_given?
      ConnectionPool.read_adapters.each do |source|
        source.query(q) do |*clauses|
          yield(*clauses)
        end
      end
    else
      # build Array of results from all sources
      # TODO: write test for sebastian's select problem
      # (without distinct, should get duplicates, they
      # were filtered out when doing results.union)
      # FIXME: Calling get_sparql_query_results? This *only* exists on the redland adapter
      results = []
      ConnectionPool.read_adapters.each do |source|
        if (q.class != String)
          source_results = source.query(q)
        else
          source_results = source.get_sparql_query_results(q, RDFS::Resource, options[:result_format])
        end
        source_results.each do |clauses|
          results << clauses
        end
      end

      # filter the empty results
      results.reject {|ary| ary.empty? }

      # remove duplicate results from multiple
      # adapters if asked for distinct query
      # (adapters return only distinct results,
      # but they cannot check duplicates against each other)
      results.uniq! if ((q.class != String) && (q.distinct?))

      # flatten results array if only one select clause
      # to prevent unnecessarily nested array [[eyal],[renaud],...]
      if (q.class != String)
        results.flatten! if (q.select_clauses.size == 1 or q.ask?)
      else
        results.flatten! if q.scan(/[?]/).length == 2
      end

      # remove array (return single value or nil) if asked to
      if options[:flatten] or ((q.class != String)  && (q.count?))
        case results.size
        when 0
          results = nil
        when 1
          results = results.first
        end
      end
    end

    results
  end # End benchmark
end