class SPARQL::Algebra::Operator::Filter
The SPARQL
GraphPattern `filter` operator.
@example
(select (?v) (project (?v) (filter (= ?v 2) (bgp (triple ?s <http://example/p> ?v)))))
Constants
- NAME
Public Instance Methods
Executes this query on the given `queryable` graph or repository. Then it passes each solution through one or more filters and removes those that evaluate to false or generate a TypeError.
Note that the last operand returns a solution set, while the first is an expression. This may be a variable, simple expression, or exprlist.
@param [RDF::Queryable] queryable
the graph or repository to query
@param [Hash{Symbol => Object}] options
any additional keyword options
@yield [solution]
each matching solution
@yieldparam [RDF::Query::Solution] solution @yieldreturn [void] ignored @return [RDF::Query::Solutions]
the resulting solution sequence
@see www.w3.org/TR/sparql11-query/#sparqlAlgebra @see www.w3.org/TR/sparql11-query/#ebv
# File lib/sparql/algebra/operator/filter.rb, line 39 def execute(queryable, **options, &block) debug(options) {"Filter #{operands.first.to_sxp}"} opts = options.merge(queryable: queryable, depth: options[:depth].to_i + 1) @solutions = RDF::Query::Solutions() queryable.query(operands.last, depth: options[:depth].to_i + 1, **options) do |solution| begin pass = boolean(operands.first.evaluate(solution, **opts)).true? debug(options) {"(filter) #{pass.inspect} #{solution.to_h.inspect}"} @solutions << solution if pass rescue debug(options) {"(filter) rescue(#{$!}): #{solution.to_h.inspect}"} end end @solutions.each(&block) if block_given? @solutions end
If
filtering a join of two BGPs (having the same graph name), don't worry about validating, for shared ndvars, anyway,
(filter (regex ?homepage "^http://example.org/" "") (join (bgp (triple ??who :homepage ?homepage)) (bgp (triple ??who :schoolHomepage ?schoolPage))))))
is legitimate
# File lib/sparql/algebra/operator/filter.rb, line 64 def validate! unless (join = operands.last).is_a?(Join) && join.operands.all? {|op| op.is_a?(RDF::Query)} && join.operands.map(&:graph_name).uniq.length == 1 operands.last.validate! end self end