Class: Redlander::Node

Inherits:
Object
  • Object
show all
Defined in:
lib/redlander/node.rb

Overview

RDF node (usually, a part of an RDF statement)

Instance Method Summary collapse

Constructor Details

#initialize(arg = nil, options = {}) ⇒ Node

Create a RDF node.

Parameters:

  • arg (Any) (defaults to: nil) —

    • an instance of URI - to create a RDF “resource”, Note that you cannot create a resource node from an URI string, it must be an instance of URI. Otherwise it is treated as a string literal.

    • nil (or absent) - to create a blank node,

    • any other Ruby object, which can be coerced into a literal.

  • options (Hash) (defaults to: {})

Options Hash (options):

  • :blank_id (String) —

    optional ID to use for a blank node.

Raises:

  • (RedlandError) —

    if it fails to create a node from the given args.



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# File 'lib/redlander/node.rb', line 60

def initialize(arg = nil, options = {})
  # If FFI::Pointer is passed, wrap it instantly,
  # because it can be freed outside before it is used here.
  @arg = arg.is_a?(FFI::Pointer) ? wrap(arg) : arg
  @options = options
end

Instance Method Details

#blank? ⇒ Boolean

Return true if node is a blank node.

Returns:

  • (Boolean) 


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# File 'lib/redlander/node.rb', line 84

def blank?
  Redland.librdf_node_is_blank(rdf_node) != 0
end

#datatype ⇒ Object

Datatype URI for the literal node, or nil



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# File 'lib/redlander/node.rb', line 36

def datatype
  if instance_variable_defined?(:@datatype)
    @datatype
  else
    @datatype = if literal?
                  rdf_uri = Redland.librdf_node_get_literal_value_datatype_uri(rdf_node)
                  rdf_uri.null? ? XmlSchema.datatype_of("") : URI.parse(Redland.librdf_uri_to_string(rdf_uri))
                else
                  nil
                end
  end
end

#eql?(other_node) ⇒ Boolean Also known as: ==

Equivalency. Only works for comparing two Nodes.

Parameters:

  • other_node (Node) —

    Node to be compared with.

Returns:

  • (Boolean) 


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# File 'lib/redlander/node.rb', line 92

def eql?(other_node)
  Redland.librdf_node_equals(rdf_node, other_node.rdf_node) != 0
end

#hash ⇒ Object 



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# File 'lib/redlander/node.rb', line 97

def hash
  self.class.hash + to_s.hash
end

#lang ⇒ Object 



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# File 'lib/redlander/node.rb', line 142

def lang
  lng = Redland.librdf_node_get_literal_value_language(rdf_node)
  lng ? lng.to_sym : nil
end

#literal? ⇒ Boolean

Return true if node is a literal.

Returns:

  • (Boolean) 


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# File 'lib/redlander/node.rb', line 77

def literal?
  Redland.librdf_node_is_literal(rdf_node) != 0
end

#rdf_node ⇒ Object

This method is part of a private API. You should avoid using this method if possible, as it may be removed or be changed in the future. 



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# File 'lib/redlander/node.rb', line 14

def rdf_node
  unless instance_variable_defined?(:@rdf_node)
    @rdf_node = case @arg
                when FFI::Pointer
                  @arg
                when NilClass
                  Redland.librdf_new_node_from_blank_identifier(Redlander.rdf_world, @options[:blank_id])
                when URI
                  Redland.librdf_new_node_from_uri_string(Redlander.rdf_world, @arg.to_s)
                else
                  value = @arg.respond_to?(:xmlschema) ? @arg.xmlschema : @arg.to_s
                  lang = @arg.respond_to?(:lang) ? @arg.lang.to_s : nil
                  dt = lang ? nil : Uri.new(XmlSchema.datatype_of(@arg)).rdf_uri
                  Redland.librdf_new_node_from_typed_literal(Redlander.rdf_world, value, lang, dt)
                end
    raise RedlandError, "Failed to create a new node" if @rdf_node.null?
    ObjectSpace.define_finalizer(self, self.class.send(:finalize_node, @rdf_node))
  end
  @rdf_node
end

#resource? ⇒ Boolean

Check whether the node is a resource (identified by a URI)

Returns:

  • (Boolean) 


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# File 'lib/redlander/node.rb', line 70

def resource?
  Redland.librdf_node_is_resource(rdf_node) != 0
end

#to_s ⇒ String

Convert this node to a string (with a datatype suffix).

Returns:

  • (String) 


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# File 'lib/redlander/node.rb', line 104

def to_s
  Redland.librdf_node_to_string(rdf_node)
end

#uri ⇒ URI?

Internal URI of the Node.

Returns the datatype URI for literal nodes, nil for blank nodes.

Returns:

  • (URI, nil) 


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# File 'lib/redlander/node.rb', line 114

def uri
  if resource?
    URI.parse(to_s[1..-2])
  elsif literal?
    datatype
  else
    nil
  end
end

#value ⇒ URI, Any

Value of the literal node as a Ruby object instance.

Returns an instance of URI for resource nodes, “blank identifier” for blank nodes.

Returns:

  • (URI, Any) 


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# File 'lib/redlander/node.rb', line 130

def value
  if resource?
    uri
  elsif blank?
    Redland.librdf_node_get_blank_identifier(rdf_node).force_encoding("UTF-8")
  else
    v = Redland.librdf_node_get_literal_value(rdf_node).force_encoding("UTF-8")
    v << "@#{lang}" if lang
    XmlSchema.instantiate(v, datatype)
  end
end