Module: RDF::Queryable
- Includes:
- Enumerable
- Included in:
- Dataset, Enumerable::Enumerator, Graph, Enumerator, Transaction
- Defined in:
- lib/rdf/mixin/queryable.rb
Overview
An RDF query mixin.
Classes that include this module should implement a ‘#query_pattern` method that yields RDF statements. Classes may also implement an optimized `#query_execute` method that yields RDF statements.
Defined Under Namespace
Classes: Enumerator
Instance Method Summary collapse
- #enum_for(method = :each, *args) ⇒ Enumerator<RDF::Statement, RDF::Query::Pattern> (also: #to_enum)
-
#first(pattern = nil) ⇒ RDF::Statement
Queries ‘self` for an RDF statement matching the given `pattern` and returns that statement if found.
-
#first_literal(pattern = nil) ⇒ RDF::Literal
Queries ‘self` for RDF statements matching the given `pattern` and returns the first found object literal.
-
#first_object(pattern = nil) ⇒ Object
Queries ‘self` for an RDF statement matching the given `pattern` and returns the statement’s object term.
-
#first_predicate(pattern = nil) ⇒ Object
Queries ‘self` for an RDF statement matching the given `pattern` and returns the statement’s predicate term.
-
#first_subject(pattern = nil) ⇒ Object
Queries ‘self` for an RDF statement matching the given `pattern` and returns the statement’s subject term.
-
#first_value(pattern = nil) ⇒ Object
Queries ‘self` for RDF statements matching the given `pattern` and returns the value of the first found object literal.
-
#query(pattern, **options) {|statement| ... } ⇒ Enumerator<RDF::Statement>, ...
Queries ‘self` for RDF statements matching the given `pattern`.
Instance Method Details
#enum_for(method = :each, *args) ⇒ Enumerator<RDF::Statement, RDF::Query::Pattern> Also known as: to_enum
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# File 'lib/rdf/mixin/queryable.rb', line 307 def enum_for(method = :each, *args) # Ensure that enumerators are, themselves, queryable this = self Queryable::Enumerator.new do |yielder| this.send(method, *args) {|*y| yielder << (y.length > 1 ? y : y.first)} end end |
#first ⇒ RDF::Statement #first(pattern) ⇒ RDF::Statement
Queries ‘self` for an RDF statement matching the given `pattern` and returns that statement if found.
Returns ‘nil` if no statements match `pattern`.
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# File 'lib/rdf/mixin/queryable.rb', line 186 def first(pattern = nil) if pattern query(pattern) do |statement| return statement end elsif respond_to?(:each_statement) each_statement do |statement| return statement end else return super() end nil end |
#first_literal ⇒ RDF::Literal #first_literal(pattern) ⇒ RDF::Literal
Queries ‘self` for RDF statements matching the given `pattern` and returns the first found object literal.
Returns ‘nil` if no statements match `pattern` or if none of the found statements have a literal as their object term.
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# File 'lib/rdf/mixin/queryable.rb', line 277 def first_literal(pattern = nil) __send__(*(pattern ? [:query, pattern] : [:each])) do |statement| return statement.object if statement.object.is_a?(RDF::Literal) end return nil end |
#first_object ⇒ RDF::Term #first_object(pattern) ⇒ RDF::Term
Queries ‘self` for an RDF statement matching the given `pattern` and returns the statement’s object term.
Returns ‘nil` if no statements match `pattern`.
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# File 'lib/rdf/mixin/queryable.rb', line 254 def first_object(pattern = nil) __send__(*(pattern ? [:query, pattern] : [:each])) do |statement| return statement.object end return nil end |
#first_predicate ⇒ RDF::URI #first_predicate(pattern) ⇒ RDF::URI
Queries ‘self` for an RDF statement matching the given `pattern` and returns the statement’s predicate term.
Returns ‘nil` if no statements match `pattern`.
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# File 'lib/rdf/mixin/queryable.rb', line 234 def first_predicate(pattern = nil) __send__(*(pattern ? [:query, pattern] : [:each])) do |statement| return statement.predicate end return nil end |
#first_subject ⇒ RDF::Resource #first_subject(pattern) ⇒ RDF::Resource
Queries ‘self` for an RDF statement matching the given `pattern` and returns the statement’s subject term.
Returns ‘nil` if no statements match `pattern`.
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# File 'lib/rdf/mixin/queryable.rb', line 214 def first_subject(pattern = nil) __send__(*(pattern ? [:query, pattern] : [:each])) do |statement| return statement.subject end return nil end |
#first_value ⇒ Object #first_value(pattern) ⇒ Object
Queries ‘self` for RDF statements matching the given `pattern` and returns the value of the first found object literal.
Returns ‘nil` if no statements match `pattern` or if none of the found statements have a literal as their object term.
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# File 'lib/rdf/mixin/queryable.rb', line 298 def first_value(pattern = nil) (literal = first_literal(pattern)) ? literal.value : nil end |
#query(pattern, **options) {|statement| ... } ⇒ Enumerator<RDF::Statement>, ...
Since 2.0, this may return an Enumerable or an Enumerator in addition to Solutions
Queries ‘self` for RDF statements matching the given `pattern`.
This method delegates to the protected #query_pattern method for the actual lower-level query pattern matching implementation.
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# File 'lib/rdf/mixin/queryable.rb', line 56 def query(pattern, **, &block) raise TypeError, "#{self} is not readable" if respond_to?(:readable?) && !readable? case pattern # A basic graph pattern (BGP) query: when Query solutions = RDF::Query::Solutions.new block = lambda {|solution| solutions << solution} unless block_given? before_query(pattern) if respond_to?(:before_query) query_execute(pattern, **, &block) after_query(pattern) if respond_to?(:after_query) # Returns the solutions, not an enumerator solutions # A simple triple/quad pattern query: else pattern = Query::Pattern.from(pattern) before_query(pattern) if respond_to?(:before_query) enum = case # Blank triple/quad patterns are equivalent to iterating over # every statement, so as a minor optimization we'll just do that # directly instead of bothering with `#query_pattern`: when pattern.blank? if block_given? each(&block) else to_a.extend(Queryable) end # Constant triple/quad patterns are equivalent to looking up a # particular statement, so as a minor optimization we'll just do # that directly instead of bothering with `#query_pattern`: when pattern.constant? statement = Statement.from(pattern) if include?(statement) if block_given? yield statement else [statement] end end # Otherwise, we delegate to `#query_pattern`: else # pattern.variable? query_pattern(pattern, **, &block) end after_query(pattern) if respond_to?(:after_query) enum end end |