class SPARQL::Algebra::Operator::Union

The SPARQL GraphPattern `union` operator.

@example

(prefix ((: <http://example/>))
  (union
    (bgp (triple ?s ?p ?o))
    (graph ?g
      (bgp (triple ?s ?p ?o)))))

@see www.w3.org/TR/sparql11-query/#sparqlAlgebra

Constants

NAME

Public Instance Methods

execute(queryable, **options, &block) click to toggle source

Executes each operand with `queryable` and performs the `union` operation by creating a new solution set consiting of all solutions from both operands.

@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

# File lib/sparql/algebra/operator/union.rb, line 34
def execute(queryable, **options, &block)
  debug(options) {"Union"}
  @solutions = RDF::Query::Solutions(operands.inject([]) do |memo, op|
    solns = op.execute(queryable, depth: options[:depth].to_i + 1, **options)
    debug(options) {"=> (op) #{solns.inspect}"}
    memo + solns
  end)
  debug(options) {"=> #{@solutions.inspect}"}
  @solutions.each(&block) if block_given?
  @solutions
end
optimize!(**options) click to toggle source

Optimizes this query.

Optimize operands and remove any which are empty.

@return [self] @see SPARQL::Algebra::Expression#optimize!

# File lib/sparql/algebra/operator/union.rb, line 64
def optimize!(**options)
  ops = operands.map {|o| o.optimize(**options) }.select {|o| o.respond_to?(:empty?) && !o.empty?}
  @operands = ops
  self
end
validate!() click to toggle source

The same blank node label cannot be used in two different basic graph patterns in the same query

Calls superclass method SPARQL::Algebra::Operator#validate!
# File lib/sparql/algebra/operator/union.rb, line 47
def validate!
  left_nodes, right_nodes = operand(0).ndvars.map(&:name), operand(1).ndvars.map(&:name)

  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