class LD::Patch::Algebra::Constraint
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.
@example existence of path solutions
(constraint (path :p)) Maps input terms to output terms using `(path :p)` returning those input terms that have at least a single solution.
@example paths with property value
(constraint (path :p) 1) Maps input terms to output terms using `(path :p)` and filters the input terms where the output term is `1`.
@example unique terms
(constraint unique) Returns the single term from the input terms if there is a single input term.
Constants
- NAME
Public Instance Methods
Source
# 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
If the first operand is :unique
@param [RDF::Queryable] queryable
the graph or repository to write
@param [Hash{Symbol => Object}] options
any additional options
@option options [Array<RDF::Term>] starting terms @return [RDF::Query::Solutions] solutions with ‘:term` mapping