Class: SPARQL::Algebra::Operator::PathZero

Inherits:
Unary show all
Includes:
Query
Defined in:
lib/sparql/algebra/operator/path_zero.rb

Overview

The SPARQL Property Path path0 (ZeroLengthPath) operator.

A zero length path matches all subjects and objects in the graph, and also any RDF terms explicitly given as endpoints of the path pattern.

See Also:

Constant Summary collapse

NAME = 
:path0

Constants inherited from Unary

Unary::ARITY

Constants inherited from SPARQL::Algebra::Operator

ARITY, IsURI, URI

Constants included from Expression

Expression::PATTERN_PARENTS

Instance Attribute Summary

Attributes included from Query

#solutions

Attributes inherited from SPARQL::Algebra::Operator

#operands

Instance Method Summary collapse

Methods included from Query

#each_solution, #empty?, #failed?, #graph_name=, #matched?, #query_yields_boolean?, #query_yields_solutions?, #query_yields_statements?, #unshift, #variables

Methods inherited from Unary

#initialize

Methods inherited from SPARQL::Algebra::Operator

#aggregate?, arity, #base_uri, base_uri, base_uri=, #bind, #boolean, #constant?, #deep_dup, #each_descendant, #eql?, #evaluatable?, evaluate, #executable?, #first_ancestor, for, #initialize, #inspect, #ndvars, #node?, #operand, #optimize, #optimize!, #parent, #parent=, #prefixes, prefixes, prefixes=, #rewrite, #to_binary, to_sparql, #to_sparql, #to_sxp, #to_sxp_bin, #validate!, #variable?, #variables, #vars

Methods included from Expression

cast, #constant?, #evaluate, extension, extension?, extensions, for, #invalid?, new, #node?, open, #optimize, #optimize!, parse, register_extension, #to_sxp_bin, #valid?, #validate!, #variable?

Constructor Details

This class inherits a constructor from SPARQL::Algebra::Operator::Unary

Instance Method Details

#execute(queryable, **options) {|solution| ... } ⇒ Object

Zero length path:

(path x (path0 :p) y) => (filter (x = y) (solution x y))

Parameters:

  • queryable (RDF::Queryable) —

    the graph or repository to query

  • options (Hash{Symbol => Object}) —

    any additional keyword options

Options Hash (**options):

Yields:

  • (solution) —

    each matching solution

Yield Parameters:

Yield Returns:

  • (void) —

    ignored

See Also:



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# File 'lib/sparql/algebra/operator/path_zero.rb', line 31

def execute(queryable, **options, &block)
  subject, object = options[:subject], options[:object]
  debug(options) {"PathZero #{[subject, operands, object].to_sse}"}

  solutions = RDF::Query::Solutions.new
  # The zero-length case implies subject == object.
  case
  when subject.variable? && object.variable?
    # Nodes is the set of all subjects and objects in queryable
    query = RDF::Query.new {|q| q.pattern({subject: subject})}
    query.execute(queryable, **options) do |solution|
      solution.merge!(object.to_sym => solution[subject])
      unless solutions.include?(solution)
        #debug(options) {"(solution-s0)-> #{solution.to_h.to_sse}"}
        solutions << solution
      end
    end if query.valid?

    # All objects which are `object`
    query = RDF::Query.new {|q| q.pattern({object: object})}
    query.execute(queryable, **options) do |solution|
      solution.merge!(subject.to_sym => solution[object])
      unless solutions.include?(solution)
        #debug(options) {"(solution-o0)-> #{solution.to_h.to_sse}"}
        solutions << solution
      end
    end if query.valid?
  when subject.variable?
    # All subjects which are `object`
    query = RDF::Query.new {|q| q.pattern({subject: object})}
    query.execute(queryable, **options) do |solution|
      solution.merge!(subject.to_sym => object)
      unless solutions.include?(solution)
        #debug(options) {"(solution-s0)-> #{solution.to_h.to_sse}"}
        solutions << solution
      end
    end if query.valid?

    # All objects which are `object`
    query = RDF::Query.new {|q| q.pattern({object: object})}
    query.execute(queryable, **options) do |solution|
      solution.merge!(subject.to_sym => object)
      unless solutions.include?(solution)
        #debug(options) {"(solution-o0)-> #{solution.to_h.to_sse}"}
        solutions << solution
      end
    end if query.valid?
  when object.variable?
    # All subjects which are `subject`
    query = RDF::Query.new {|q| q.pattern({subject: subject})}
    query.execute(queryable, **options) do |solution|
      solution.merge!(object.to_sym => subject)
      unless solutions.include?(solution)
        #debug(options) {"(solution-s0)-> #{solution.to_h.to_sse}"}
        solutions << solution
      end
    end if query.valid?

    # All objects which are `subject`
    query = RDF::Query.new {|q| q.pattern({object: subject})}
    query.execute(queryable, **options) do |solution|
      solution.merge!(object.to_sym => subject)
      unless solutions.include?(solution)
        #debug(options) {"(solution-o0)-> #{solution.to_h.to_sse}"}
        solutions << solution
      end
    end if query.valid?
  else
    # Otherwise, if subject == object, an empty solution
    solutions << RDF::Query::Solution.new if subject == object
  end

  solutions.uniq!
  debug(options) {"(path0)=> #{solutions.to_sxp}"}
  solutions.each(&block) if block_given?
  solutions
end