Class: SPARQL::Algebra::Operator::Extend

Inherits:
Binary show all
Includes:
Query
Defined in:
vendor/bundler/ruby/2.7.0/bundler/gems/sparql-cd4915d97d78/lib/sparql/algebra/operator/extend.rb

Overview

The SPARQL Extend operator.

Extends a solution

Examples:

(select (?z)
  (project (?z)
    (extend ((?z (+ ?o 10)))
      (bgp (triple ?s <http://example/p> ?o)))))

See Also:

Constant Summary collapse

NAME = 
[:extend]

Constants inherited from Binary

Binary::ARITY

Constants inherited from SPARQL::Algebra::Operator

ARITY, IsURI, URI

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 Binary

#initialize

Methods inherited from SPARQL::Algebra::Operator

#aggregate?, arity, #base_uri, base_uri, base_uri=, #bind, #boolean, #constant?, #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_sxp, #to_sxp_bin, #variable?, #vars

Methods included from Expression

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

Constructor Details

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

Instance Method Details

#execute(queryable, **options) {|solution| ... } ⇒ RDF::Query::Solutions

Let μ be a solution mapping, Ω a multiset of solution mappings, var a variable and expr be an expression, then we define:

Extend(μ, var, expr) = μ ∪ { (var,value) | var not in dom(μ) and value = expr(μ) }

Extend(μ, var, expr) = μ if var not in dom(μ) and expr(μ) is an error

Extend is undefined when var in dom(μ).

Extend(Ω, var, expr) = { Extend(μ, var, expr) | μ in Ω }

For SPARQL*, expr may be an embedded tiple pattern

(extend ((?t (triple ?bob foaf:age ?age))) (bgp (triple ?t dct:source ?src)))

Parameters:

Yields:

  • (solution) —

    each matching solution

Yield Parameters:

Yield Returns:

  • (void) —

    ignored

Returns:

See Also:



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# File 'vendor/bundler/ruby/2.7.0/bundler/gems/sparql-cd4915d97d78/lib/sparql/algebra/operator/extend.rb', line 48

def execute(queryable, **options, &block)
  debug(options) {"Extend"}
  @solutions = operand(1).execute(queryable, depth: options[:depth].to_i + 1, **options)
  @solutions.each do |solution|
    debug(options) {"===> soln #{solution.to_h.inspect}"}
    operand(0).each do |(var, expr)|
      begin
        val = expr.evaluate(solution, queryable: queryable,
                                      depth: options[:depth].to_i + 1,
                                      **options)
        debug(options) {"===> + #{var} => #{val.inspect}"}
        solution.bindings[var.to_sym] = if val.is_a?(RDF::Query::Pattern)
          # Variable is bound to the solution
          val.bind(solution)
        else
          val
        end
      rescue TypeError => e
        # Evaluates to error, ignore
        debug(options) {"===> #{var} error: #{e.message}"}
      end
    end
  end
  @solutions.each(&block) if block_given?
  @solutions
end

#validate! ⇒ Object

The variable introduced by the BIND clause must not have been used in the group graph pattern up to the point of use in BIND



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# File 'vendor/bundler/ruby/2.7.0/bundler/gems/sparql-cd4915d97d78/lib/sparql/algebra/operator/extend.rb', line 76

def validate!
  bind_vars = operand(0).map(&:first).map(&:name)
  query_vars = operand(1).vars.map(&:name)
  
  unless (bind_vars.compact & query_vars.compact).empty?
    raise ArgumentError,
         "bound variable used in query: #{(bind_vars.compact & query_vars.compact).to_sse}"
  end
  super
end