class RDF::Query::Pattern
An RDF query pattern.
Attributes
The estimated cost of this pattern (for query optimization).
@return [Numeric]
Any additional options for this pattern.
@return [Hash]
Public Class Methods
@private @since 0.2.2
# File lib/rdf/query/pattern.rb, line 8 def self.from(pattern, options = {}) case pattern when Pattern then pattern when Array, Statement self.new(pattern[0], pattern[1], pattern[2], options.merge(graph_name: pattern[3])) when Hash then self.new(options.merge(pattern)) else raise ArgumentError, "expected RDF::Query::Pattern, RDF::Statement, Hash, or Array, but got #{pattern.inspect}" end end
@overload initialize(options = {})
@param [Hash{Symbol => Object}] options @option options [Variable, Resource, Symbol, nil] :subject (nil) @option options [Variable, URI, Symbol, nil] :predicate (nil) @option options [Variable, Term, Symbol, nil] :object (nil) @option options [Variable, Resource, Symbol, nil, false] :graph_name (nil) A graph_name of nil matches any graph, a graph_name of false, matches only the default graph. @option options [Boolean] :optional (false)
@overload initialize(subject, predicate, object, options = {})
@param [Variable, Resource, Symbol, nil] subject @param [Variable, URI, Symbol, nil] predicate @param [Variable, Termm, Symbol, nil] object @param [Hash{Symbol => Object}] options @option options [Variable, Resource, Symbol, nil, false] :graph_name (nil) A graph_name of nil matches any graph, a graph_name of false, matches only the default graph. @option options [Boolean] :optional (false)
@note {Statement} treats symbols as interned {Node} instances, in a {Pattern}, they are treated as {Variable}.
# File lib/rdf/query/pattern.rb, line 38 def initialize(subject = nil, predicate = nil, object = nil, options = {}) super end
Public Instance Methods
Binds the pattern to a solution, making it no longer variable if all variables are resolved to bound variables
@param [RDF::Query::Solution] solution @return [self]
# File lib/rdf/query/pattern.rb, line 253 def bind(solution) self.to_quad.each_with_index do |term, index| if term && term.variable? && solution[term] self[index] = solution[term] end end self end
Returns the number of bindings in this pattern.
@return [Integer] (0..3)
# File lib/rdf/query/pattern.rb, line 274 def binding_count bindings.size end
Returns all bindings in this pattern.
@return [Hash{Symbol => RDF::Term}]
# File lib/rdf/query/pattern.rb, line 282 def bindings bindings = {} bindings.merge!(subject.bindings) if subject.is_a?(Variable) bindings.merge!(predicate.bindings) if predicate.is_a?(Variable) bindings.merge!(object.bindings) if object.is_a?(Variable) bindings.merge!(graph_name.bindings) if graph_name.is_a?(Variable) bindings end
Returns `true` if this pattern contains bindings.
@return [Boolean] `true` or `false`
# File lib/rdf/query/pattern.rb, line 266 def bindings? !bindings.empty? end
Returns `true` if this is a blank pattern, with all terms being `nil`.
@return [Boolean] `true` or `false` @since 0.3.0
# File lib/rdf/query/pattern.rb, line 69 def blank? subject.nil? && predicate.nil? && object.nil? && graph_name.nil? end
Returns `true` if all variables in this pattern are bound.
@return [Boolean] `true` or `false`
# File lib/rdf/query/pattern.rb, line 295 def bound? !variables.empty? && variables.values.all?(&:bound?) end
Returns all bound variables in this pattern.
@return [Hash{Symbol => Variable}]
# File lib/rdf/query/pattern.rb, line 303 def bound_variables variables.reject { |name, variable| variable.unbound? } end
Executes this query pattern on the given `queryable` object.
Values are matched using using Queryable#query_pattern.
If the optional `bindings` are given, variables will be substituted with their values when executing the query.
To match triples only in the default graph, set graph_name to `false`.
@example
Pattern.new(:s, :p, :o).execute(RDF::Repository.load('etc/doap.nt'))
@param [RDF::Queryable] queryable
the graph or repository to query
@param [Hash{Symbol => RDF::Term}] bindings
optional variable bindings to use
@yield [statement]
each matching statement
@yieldparam [RDF::Statement] statement
an RDF statement matching this pattern
@return [Enumerable<RDF::Query::Pattern>]
an enumerator yielding matching statements
@see RDF::Queryable#query @since 0.3.0
# File lib/rdf/query/pattern.rb, line 137 def execute(queryable, bindings = {}, &block) query = { subject: subject.is_a?(Variable) && bindings[subject.to_sym] ? bindings[subject.to_sym] : subject, predicate: predicate.is_a?(Variable) && bindings[predicate.to_sym] ? bindings[predicate.to_sym] : predicate, object: object.is_a?(Variable) && bindings[object.to_sym] ? bindings[object.to_sym] : object, graph_name: graph_name.is_a?(Variable) && bindings[graph_name.to_sym] ? bindings[graph_name.to_sym] : graph_name, }.delete_if{|k,v| v.nil?} # Do all the variable terms refer to distinct variables? variables = self.variables if variable_count == variables.size # If so, we can just let the repository implementation handle # everything and yield matching statements directly: queryable.query(query, &block) # No, some terms actually refer to the same variable... else # Figure out which terms refer to the same variable: terms = variables.each_key.find do |name| terms = variable_terms(name) break terms if terms.size > 1 end queryable.query(query).select do |statement| # Only yield those matching statements where the variable # constraint is also satisfied: # FIXME: `Array#uniq` uses `#eql?` and `#hash`, not `#==` if terms.map { |term| statement.send(term) }.uniq.size.equal?(1) yield statement if block_given? true end end end end
Returns `true` if this pattern contains any variables.
@return [Boolean] `true` or `false` @since 0.3.0
# File lib/rdf/query/pattern.rb, line 78 def has_variables? subject.is_a?(Variable) || predicate.is_a?(Variable) || object.is_a?(Variable) || graph_name.is_a?(Variable) end
@private
# File lib/rdf/query/pattern.rb, line 44 def initialize! @graph_name = Variable.new(@graph_name) if @graph_name.is_a?(Symbol) @subject = Variable.new(@subject) if @subject.is_a?(Symbol) @predicate = Variable.new(@predicate) if @predicate.is_a?(Symbol) @object = Variable.new(@object) if @object.is_a?(Symbol) super end
Returns `true` if this is an optional pattern.
@example
Pattern.new(:s, :p, :o).optional? #=> false Pattern.new(:s, :p, :o, optional: true).optional? #=> true
@return [Boolean] `true` or `false` @since 0.3.0
# File lib/rdf/query/pattern.rb, line 95 def optional? !!options[:optional] end
Returns a query solution constructed by binding any variables in this pattern with the corresponding terms in the given `statement`.
@example
pattern = Pattern.new(:s, :p, :o) solution = pattern.solution(statement) pattern[:s] #=> statement.subject pattern[:p] #=> statement.predicate pattern[:o] #=> statement.object
@param [RDF::Statement] statement
an RDF statement to bind terms from
@return [RDF::Query::Solution] @since 0.3.0
# File lib/rdf/query/pattern.rb, line 187 def solution(statement) RDF::Query::Solution.new do |solution| solution[subject.to_sym] = statement.subject if subject.is_a?(Variable) solution[predicate.to_sym] = statement.predicate if predicate.is_a?(Variable) solution[object.to_sym] = statement.object if object.is_a?(Variable) solution[graph_name.to_sym] = statement.graph_name if graph_name.is_a?(Variable) end end
Returns a string representation of this pattern.
@return [String]
# File lib/rdf/query/pattern.rb, line 327 def to_s StringIO.open do |buffer| # FIXME in RDF::Statement buffer << 'OPTIONAL ' if optional? buffer << [subject, predicate, object].map do |r| r.is_a?(RDF::Query::Variable) ? r.to_s : RDF::NTriples.serialize(r) end.join(" ") buffer << case graph_name when nil, false then " ." when Variable then " #{graph_name.to_s} ." else " #{RDF::NTriples.serialize(graph_name)} ." end buffer.string end end
Returns `true` if all variables in this pattern are unbound.
@return [Boolean] `true` or `false`
# File lib/rdf/query/pattern.rb, line 311 def unbound? !variables.empty? && variables.values.all?(&:unbound?) end
Returns all unbound variables in this pattern.
@return [Hash{Symbol => Variable}]
# File lib/rdf/query/pattern.rb, line 319 def unbound_variables variables.reject { |name, variable| variable.bound? } end
Is this pattern composed only of valid components?
@return [Boolean] `true` or `false`
# File lib/rdf/query/pattern.rb, line 103 def valid? (has_subject? ? (subject.resource? || subject.variable?) && subject.valid? : true) && (has_predicate? ? (predicate.uri? || predicate.variable?) && predicate.valid? : true) && (has_object? ? (object.term? || object.variable?) && object.valid? : true) && (has_graph? ? (graph_name.resource? || graph_name.variable?) && graph_name.valid? : true ) rescue NoMethodError false end
Returns the number of variables in this pattern.
Note: this does not count distinct variables, and will therefore e.g. return 3 even if two terms are actually the same variable.
@return [Integer] (0..3)
# File lib/rdf/query/pattern.rb, line 222 def variable_count count = 0 count += 1 if subject.is_a?(Variable) count += 1 if predicate.is_a?(Variable) count += 1 if object.is_a?(Variable) count += 1 if graph_name.is_a?(Variable) count end
Returns the variable terms in this pattern.
@example
Pattern.new(RDF::Node.new, :p, 123).variable_terms #=> [:predicate]
@param [Symbol, to_sym] name
an optional variable name
@return [Array<Symbol>] @since 0.3.0
# File lib/rdf/query/pattern.rb, line 206 def variable_terms(name = nil) terms = [] terms << :subject if subject.is_a?(Variable) && (!name || name.eql?(subject.name)) terms << :predicate if predicate.is_a?(Variable) && (!name || name.eql?(predicate.name)) terms << :object if object.is_a?(Variable) && (!name || name.eql?(object.name)) terms << :graph_name if graph_name.is_a?(Variable) && (!name || name.eql?(graph_name.name)) terms end
Returns all variables in this pattern.
Note: this returns a hash containing distinct variables only.
@return [Hash{Symbol => Variable}]
# File lib/rdf/query/pattern.rb, line 239 def variables variables = {} variables.merge!(subject.variables) if subject.is_a?(Variable) variables.merge!(predicate.variables) if predicate.is_a?(Variable) variables.merge!(object.variables) if object.is_a?(Variable) variables.merge!(graph_name.variables) if graph_name.is_a?(Variable) variables end