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) ⇒ Object

add triple s,p,o to the currently selected write-adapter

Raises:



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# File 'lib/active_rdf/federation/federation_manager.rb', line 8

def FederationManager.add(s,p,o)
  # 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)
end

.delete(s, p, o = :all) ⇒ Object

delete triple s,p,o from the currently selected write adapter (s and p are mandatory, o is optional, symbols are interpreted as wildcards)

Raises:



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# File 'lib/active_rdf/federation/federation_manager.rb', line 16

def FederationManager.delete(s,p,o=:all)
  raise ActiveRdfError, "cannot write without a write-adapter" unless ConnectionPool.write_adapter
  ConnectionPool.write_adapter.delete(s,p,o)
end

.query(q, options = {:flatten => true}) ⇒ 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 24

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

  # 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)
    results = []
    ConnectionPool.read_adapters.each do |source|
		source_results = source.query(q)
		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.distinct?

    # flatten results array if only one select clause
    # to prevent unnecessarily nested array [[eyal],[renaud],...]
    results.flatten! if q.select_clauses.size == 1 or q.ask?

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