Ruby Jing¶ ↑

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RELAX NG schema validation using the Jing CLI

require "jing"

jing = Jing.new("schema.rng")
begin
  errors = jing.validate("doc.xml")
rescue Jing::Error => e
  abort "what what what #{e}"
end

if errors.none?
  puts "Valid!"
else
  errors.each do |error|
    puts "#{error[:message]} @ #{error[:line]}:#{error[:column]}"
  end
end

# This can also raise errors
abort "Invalid!" unless jing.valid?("/path/to/doc.xml")

Simple: good error messages. Let’s look at the error messages provided by each of these libraries.

<!-- RNG schema -->
<element name="addressBook" xmlns="http://relaxng.org/ns/structure/1.0">
  <zeroOrMore>
    <element name="card">
      <attribute name="version">
        <choice>
          <value>v1</value>
          <value>v2</value>
        </choice>
      </attribute>
      <element name="name">
        <text/>
      </element>
    </element>
  </zeroOrMore>
</element>

<!-- XML A -->
<addressBook>
  <card></card>
</addressBook>

<!-- XML B -->
<addressBook>
  <card verison="v100">
    <name>John Smith</name>
    <oops>Doh!</oops>
  </card>
</addressBook>

schema = Nokogiri::XML::RelaxNG(File.read(rng))
doc = Nokogiri::XML(File.read(xml))
errors = schema.validate(doc)
errors.each { |e| puts e }

Resulting errors:

# XML A
Element card failed to validate attributes
Expecting an element , got nothing

# XML B
Element card failed to validate attributes
Did not expect element oops there

include REXML
doc = Document.new(File.read(xml))
validator = Validation::RelaxNG.new(File.read(rng))
validator.validate(doc)

Fails for XML A and XML B –it treats the XML declaration as a validation error!

Validation error.  Expected: :start_element( addressBook ) from < S.1 #:start_element( addressBook ), < Z.2 #:start_element( card ), :start_attribute( version ), < C.3 :text( v1 ) or :text( v2 ) >, :end_attribute(  ), :start_element( name ), :text(  ), :end_element(  ), :start_element( email ), :text(  ), :end_element(  ), :end_element(  ) >, :end_element(  ), :end_document(  ) >  but got <?xml ... ?>(
 )

jing = Jing.new(schema)
errors = jing.validate(xml)
errors.each { |e| puts e[:message] }

Resulting errors:

# XML A
element "card" missing required attribute "version"
element "card" incomplete; missing required element "name"

# XML B
value of attribute "version" is invalid; must be equal to "v1" or "v2"
element "oops" not allowed anywhere; expected the element end-tag

Better, don’t ya think?

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Skye Shaw [skye.shaw AT gmail.com]

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