Class: JSON::LD::Writer

Inherits:
RDF::Writer
  • Object
show all
Includes:
StreamingWriter, Utils
Defined in:
lib/json/ld/writer.rb

Overview

A JSON-LD parser in Ruby.

Note that the natural interface is to write a whole graph at a time. Writing statements or Triples will create a graph to add them to and then serialize the graph.

The writer will add prefix definitions, and use them for creating @context definitions, and minting CURIEs

Select the :expand option to output JSON-LD in expanded form

Examples:

Obtaining a JSON-LD writer class

RDF::Writer.for(:jsonld)         #=> JSON::LD::Writer
RDF::Writer.for("etc/test.json")
RDF::Writer.for(:file_name      => "etc/test.json")
RDF::Writer.for(file_extension: "json")
RDF::Writer.for(:content_type   => "application/turtle")

Serializing RDF graph into an JSON-LD file

JSON::LD::Writer.open("etc/test.json") do |writer|
  writer << graph
end

Serializing RDF statements into an JSON-LD file

JSON::LD::Writer.open("etc/test.json") do |writer|
  graph.each_statement do |statement|
    writer << statement
  end
end

Serializing RDF statements into an JSON-LD string

JSON::LD::Writer.buffer do |writer|
  graph.each_statement do |statement|
    writer << statement
  end
end

Creating @@context prefix definitions in output

JSON::LD::Writer.buffer(
  prefixes: {
    nil => "http://example.com/ns#",
    foaf: "http://xmlns.com/foaf/0.1/"}
) do |writer|
  graph.each_statement do |statement|
    writer << statement
  end
end

See Also:

Author:

Instance Attribute Summary collapse

Instance Method Summary collapse

Methods included from Utils

#add_value, #as_resource, #blank_node?, #compare_values, #has_property, #has_value, #index?, #list?, #node?, #node_reference?, #value?

Methods included from StreamingWriter

#stream_epilogue, #stream_prologue, #stream_statement

Constructor Details

#initialize(output = $stdout, options = {}) {|writer| ... } ⇒ Writer

Initializes the RDF-LD writer instance.

Parameters:

  • output (IO, File) (defaults to: $stdout) —

    the output stream

  • options (Hash{Symbol => Object}) (defaults to: {}) —

    any additional options

Options Hash (options):

  • :encoding (Encoding) — default: Encoding::UTF_8 —

    the encoding to use on the output stream (Ruby 1.9+)

  • :canonicalize (Boolean) — default: false —

    whether to canonicalize literals when serializing

  • :prefixes (Hash) — default: {} —

    the prefix mappings to use (not supported by all writers)

  • :standard_prefixes (Boolean) — default: false —

    Add standard prefixes to @prefixes, if necessary.

  • :context (IO, Array, Hash, String, Context) — default: {} —

    context to use when serializing. Constructed context for native serialization.

  • :frame (IO, Array, Hash, String, Context) — default: {} —

    frame to use when serializing.

  • :unique_bnodes (Boolean) — default: false —

    Use unique bnode identifiers, defaults to using the identifier which the node was originall initialized with (if any).

  • :stream (Boolean) — default: false —

    Do not attempt to optimize graph presentation, suitable for streaming large graphs.

Yields:

  • (writer) —

    ‘self`

  • (writer)

Yield Parameters:

  • writer (RDF::Writer)
  • writer (RDF::Writer)

Yield Returns:

  • (void) 


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# File 'lib/json/ld/writer.rb', line 95

def initialize(output = $stdout, options = {}, &block)
  options[:base_uri] ||= options[:base] if options.has_key?(:base)
  options[:base] ||= options[:base_uri] if options.has_key?(:base_uri)
  super do
    @repo = RDF::Repository.new
    @debug = @options[:debug]

    if block_given?
      case block.arity
        when 0 then instance_eval(&block)
        else block.call(self)
      end
    end
  end
end

Instance Attribute Details

#context ⇒ Context (readonly)

Returns context used to load and administer contexts.

Returns:

  • (Context) —

    context used to load and administer contexts



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# File 'lib/json/ld/writer.rb', line 65

def context
  @context
end

#graph ⇒ RDF::Graph (readonly)

Returns Graph of statements serialized.

Returns:

  • (RDF::Graph) —

    Graph of statements serialized



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# File 'lib/json/ld/writer.rb', line 61

def graph
  @graph
end

Instance Method Details

#write_epilogue ⇒ void

This method returns an undefined value.

Outputs the Serialized JSON-LD representation of all stored statements.

If provided a context or prefixes, we’ll create a context and use it to compact the output. Otherwise, we return un-compacted JSON-LD

See Also:



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# File 'lib/json/ld/writer.rb', line 157

def write_epilogue
  return stream_epilogue if @options[:stream]

  debug("writer") { "serialize #{@repo.count} statements, #{@options.inspect}"}
  result = API.fromRdf(@repo, @options)

  # If we were provided a context, or prefixes, use them to compact the output
  context = RDF::Util::File.open_file(@options[:context]) if @options[:context].is_a?(String)
  context ||= @options[:context]
  context ||= if @options[:prefixes] || @options[:language] || @options[:standard_prefixes]
    ctx = Context.new(@options)
    ctx.language = @options[:language] if @options[:language]
    @options[:prefixes].each do |prefix, iri|
      ctx.set_mapping(prefix, iri) if prefix && iri
    end if @options[:prefixes]
    ctx
  end

  # Rename BNodes to uniquify them, if necessary
  if options[:unique_bnodes]
    result = API.flatten(result, context, @options)
  end

  frame = RDF::Util::File.open_file(@options[:frame]) if @options[:frame].is_a?(String)
  if frame ||= @options[:frame]
    # Perform framing, if given a frame
    debug("writer") { "frame result"}
    result = API.frame(result, frame, @options)
  elsif context
    # Perform compaction, if we have a context
    debug("writer") { "compact result"}
    result = API.compact(result, context,  @options)
  end

  @output.write(result.to_json(JSON_STATE))
end

#write_prologue ⇒ void

This method returns an undefined value.

Necessary for streaming



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# File 'lib/json/ld/writer.rb', line 140

def write_prologue
  case
  when @options[:stream]
    stream_prologue
  else
    super
  end
end

#write_statement(statement) ⇒ void

This method returns an undefined value.

Adds a statement to be serialized

Parameters:

  • statement (RDF::Statement) 


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# File 'lib/json/ld/writer.rb', line 115

def write_statement(statement)
  case
  when @options[:stream]
    stream_statement(statement)
  else
    # Add to repo and output in epilogue
    @repo.insert(statement)
  end
end

#write_triple(subject, predicate, object) ⇒ void

This method is abstract.

This method returns an undefined value.

Addes a triple to be serialized

Parameters:

  • subject (RDF::Resource)
  • predicate (RDF::URI)
  • object (RDF::Value)

Raises:

  • (NotImplementedError) —

    unless implemented in subclass



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# File 'lib/json/ld/writer.rb', line 133

def write_triple(subject, predicate, object)
  write_statement(Statement.new(subject, predicate, object))
end