class SPARQL::Algebra::Operator::LeftJoin
The SPARQL
GraphPattern `leftjoin` operator.
@example
(prefix ((: <http://example/>)) (leftjoin (bgp (triple ?x :p ?v)) (bgp (triple ?y :q ?w)) (= ?v 2)))
Constants
- NAME
Public Instance Methods
Executes each operand with `queryable` and performs the `leftjoin` operation by adding every solution from the left, merging compatible solutions from the right that match an optional filter.
@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.rubydoc.info/github/ruby-rdf/rdf/RDF/Query/Solution#merge-instance_method @see www.rubydoc.info/github/ruby-rdf/rdf/RDF/Query/Solution#compatible%3F-instance_method
# File lib/sparql/algebra/operator/left_join.rb, line 37 def execute(queryable, **options, &block) filter = operand(2) raise ArgumentError, "leftjoin operator accepts at most two arguments with an optional filter" if operands.length < 2 || operands.length > 3 debug(options) {"LeftJoin"} left = queryable.query(operand(0), depth: options[:depth].to_i + 1, **options) debug(options) {"=>(leftjoin left) #{left.inspect}"} right = queryable.query(operand(1), depth: options[:depth].to_i + 1, **options) debug(options) {"=>(leftjoin right) #{right.inspect}"} # LeftJoin(Ω1, Ω2, expr) = @solutions = RDF::Query::Solutions() left.each do |s1| load_left = true right.each do |s2| s = s2.merge(s1) expr = filter ? boolean(filter.evaluate(s)).true? : true rescue false debug(options) {"===>(evaluate) #{s.inspect}"} if filter if expr && s1.compatible?(s2) # { merge(μ1, μ2) | μ1 in Ω1 and μ2 in Ω2, and μ1 and μ2 are compatible and expr(merge(μ1, μ2)) is true } debug(options) {"=>(merge s1 s2) #{s.inspect}"} @solutions << s load_left = false # Left solution added one or more times due to merge end end if load_left debug(options) {"=>(add) #{s1.inspect}"} @solutions << s1 end end debug(options) {"=> #{@solutions.inspect}"} @solutions.each(&block) if block_given? @solutions end
Optimizes this query.
If
optimize operands, and if the first two operands are both Queries, replace with the unique sum of the query elements
@return [Object] a copy of `self` @see SPARQL::Algebra::Expression#optimize
FIXME
# File lib/sparql/algebra/operator/left_join.rb, line 98 def optimize!(**options) return self ops = operands.map {|o| o.optimize(**options) }.select {|o| o.respond_to?(:empty?) && !o.empty?} expr = ops.pop unless ops.last.executable? expr = nil if expr.respond_to?(:true?) && expr.true? # ops now is one or two executable operators # expr is a filter expression, which may have been optimized to 'true' case ops.length when 0 RDF::Query.new # Empty query, expr doesn't matter when 1 expr ? Filter.new(expr, ops.first) : ops.first else expr ? LeftJoin.new(ops[0], ops[1], expr) : LeftJoin.new(ops[0], ops[1]) end end
The same blank node label cannot be used in two different basic graph patterns in the same query
SPARQL::Algebra::Operator#validate!
# File lib/sparql/algebra/operator/left_join.rb, line 79 def validate! left_nodes, right_nodes = operand(0).ndvars, operand(1).ndvars unless (left_nodes.compact & right_nodes.compact).empty? raise ArgumentError, "sub-operands share non-distinguished variables: #{(left_nodes.compact & right_nodes.compact).to_sse}" end super end