Method: RDF::Queryable#query

Defined in:
lib/rdf/mixin/queryable.rb

#query(pattern, **options) {|statement| ... } ⇒ Enumerator<RDF::Statement>, ...

Note:

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.

Examples:

Querying for statements having a given predicate

queryable.query([nil, RDF::Vocab::DOAP.developer, nil])
queryable.query({predicate: RDF::Vocab::DOAP.developer}) do |statement|
  puts statement.inspect
end

Querying for solutions from a BGP

query = RDF::Query.new {pattern [:s, :p, :o]}
queryable.query(query) do |solution|
  puts solution.inspect
end

Parameters:

  • pattern (RDF::Query, RDF::Statement, Array(RDF::Term), Hash)
  • options (Hash{Symbol => Object}) —

    ({}) Any other options passed to #query_pattern or #query_execute

Yields:

  • (statement) —

    each matching statement

Yield Parameters:

Yield Returns:

  • (void) —

    ignored

Returns:

Raises:

  • (TypeError)

See Also:

  • #query_pattern


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# File 'lib/rdf/mixin/queryable.rb', line 56

def query(pattern, **options, &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, **options, &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, **options, &block)
      end
      after_query(pattern) if respond_to?(:after_query)
      enum
  end
end