Class: LD::Patch::Algebra::Constraint

Inherits:
SPARQL::Algebra::Operator
  • Object
show all
Includes:
SPARQL::Algebra::Evaluatable, SPARQL::Algebra::Query
Defined in:
lib/ld/patch/algebra/constraint.rb

Overview

The LD Patch constraint operator.

A constraint is a query operator which either ensures that there is a single input node (“!” operator) or finds a set of nodes for a given path, optionally filtering those nodes with a particular predicate value.

Maps input terms to output terms using (path :p) returning those input terms that have at least a single solution.

Maps input terms to output terms using (path :p) and filters the input terms where the output term is 1.

Returns the single term from the input terms if there is a single input term.

Examples:

existence of path solutions

(constraint (path :p))

paths with property value

(constraint (path :p) 1)

unique terms


(constraint unique)

Constant Summary collapse

NAME = 
:constraint

Instance Method Summary collapse

Instance Method Details

#execute(queryable, options = {}) ⇒ RDF::Query::Solutions

If the first operand is :unique

Parameters:

  • queryable (RDF::Queryable) —

    the graph or repository to write

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

    any additional options

Options Hash (options):

  • starting (Array<RDF::Term>) —

    terms

Returns:

  • (RDF::Query::Solutions) —

    solutions with :term mapping



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# File 'lib/ld/patch/algebra/constraint.rb', line 38

def execute(queryable, options = {})
  debug(options) {"Constraint"}
  terms = Array(options.fetch(:terms))
  op, value = operands

  results = if op == :unique
    terms.length == 1 ? terms : []
  else
    # op is a path, filter input terms based on the presense or absense of output terms. Additionally, if a constraint value is given, output terms must equal that value
    terms.select do |term|
      output_terms = op.execute(queryable, options.merge(terms: [term])).map(&:path)
      output_terms = output_terms.select {|t| t == value} if value
      !output_terms.empty?
    end
  end
  RDF::Query::Solutions.new(results.map {|t| RDF::Query::Solution.new(path: t)})
end