Class: RDF::N3::Algebra::ListOperator

Inherits:
SPARQL::Algebra::Operator::Binary
  • Object
show all
Includes:
Builtin, SPARQL::Algebra::Query, SPARQL::Algebra::Update
Defined in:
lib/rdf/n3/algebra/list_operator.rb

Overview

This is a generic operator where the subject is a list or binds to a list and the object is either a constant that equals the evaluation of the subject, or a variable to which the result is bound in a solution

Constant Summary collapse

NAME = 
:listOperator

Instance Attribute Summary

Attributes included from Enumerable

#existentials, #universals

Instance Method Summary collapse

Methods included from Builtin

#each, #evaluate, #hash, #rank, #to_uri

Instance Method Details

#as_literal(object) ⇒ Object

Returns a literal for the numeric argument.



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# File 'lib/rdf/n3/algebra/list_operator.rb', line 85

def as_literal(object)
  case object
  when Float
    literal = RDF::Literal(object, canonicalize: true)
    literal.instance_variable_set(:@string, literal.to_s.downcase)
    literal
  else
    RDF::Literal(object, canonicalize: true)
  end
end

#execute(queryable, solutions:, **options) ⇒ RDF::Query::Solutions

The operator takes a list and provides a mechanism for subclasses to operate over (and validate) that list argument.

Parameters:

  • queryable (RDF::Queryable) —

    the graph or repository to query

  • solutions (RDF::Query::Solutions) —

    solutions for chained queries

Returns:

  • (RDF::Query::Solutions) 


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# File 'lib/rdf/n3/algebra/list_operator.rb', line 19

def execute(queryable, solutions:, **options)
  RDF::Query::Solutions(solutions.map do |solution|
    # Might be a variable or node evaluating to a list in queryable, or might be a list with variables
    subject = operand(0).evaluate(solution.bindings, formulae: formulae)
    next unless subject
    # If it evaluated to a BNode, re-expand as a list
    subject = RDF::N3::List.try_list(subject, queryable).evaluate(solution.bindings, formulae: formulae)
    object = operand(1).evaluate(solution.bindings, formulae: formulae) || operand(1)
    object = formulae.fetch(object, object) if object.node?

    log_info(self.class.const_get(:NAME), "subject") {SXP::Generator.string(subject.to_sxp_bin).strip}
    log_info(self.class.const_get(:NAME), "object") {SXP::Generator.string(object.to_sxp_bin).strip}
    next unless validate(subject)

    lhs = resolve(subject)
    if lhs.nil?
      log_error(self.class.const_get(:NAME), "subject evaluates to null") {subject.inspect}
      next
    end

    if object.variable?
      log_debug(self.class.const_get(:NAME), "result") {SXP::Generator.string(lhs.to_sxp_bin).strip}
      solution.merge(object.to_sym => lhs)
    elsif object != lhs
      log_debug(self.class.const_get(:NAME), "result: false")
      nil
    else
      log_debug(self.class.const_get(:NAME), "result: true")
      solution
    end
  end.compact.uniq)
end

#input_operand ⇒ RDF::Term

Input is generically the subject

Returns:



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# File 'lib/rdf/n3/algebra/list_operator.rb', line 56

def input_operand
  operand(0)
end

#resolve(list) ⇒ RDF::Term

Subclasses implement ‘resolve`.

Parameters:

Returns:

Raises:



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# File 'lib/rdf/n3/algebra/list_operator.rb', line 65

def resolve(list)
  raise NotImplemented
end

#validate(list) ⇒ Boolean

Subclasses may override or supplement validate to perform validation on the list subject

Parameters:

Returns:

  • (Boolean) 


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# File 'lib/rdf/n3/algebra/list_operator.rb', line 74

def validate(list)
  if list.list? && list.valid?
    true
  else
    log_error(NAME) {"operand is not a list: #{list.to_sxp}"}
    false
  end
end