Nokogiri builder can be used for building XML and HTML documents.

Synopsis:

  builder = Nokogiri::XML::Builder.new do |xml|
    xml.root {
      xml.products {
        xml.widget {
          xml.id_ "10"
          xml.name "Awesome widget"
        }
      }
    }
  end
  puts builder.to_xml

Builder scope

The builder allows two forms. When the builder is supplied with a block that has a parameter, the outside scope is maintained. This means you can access variables that are outside your builder. If you don’t need outside scope, you can use the builder without the “xml” prefix like this:

  builder = Nokogiri::XML::Builder.new do
    root {
      products {
        widget {
          id_ "10"
          name "Awesome widget"
        }
      }
    }
  end

Special Tags

The builder works by taking advantage of method_missing. Unfortunately some methods are defined in ruby that are difficult or dangerous to remove. You may want to create tags with the name “type”, “class”, and “id” for example. In that case, you can use an underscore to disambiguate your tag name from the method call.

Here is an example of using the underscore to disambiguate tag names from ruby methods:

  @objects = [Object.new, Object.new, Object.new]

  builder = Nokogiri::XML::Builder.new do |xml|
    xml.root {
      xml.objects {
        @objects.each do |o|
          xml.object {
            xml.type_   o.type
            xml.class_  o.class.name
            xml.id_     o.id
          }
        end
      }
    }
  end
  puts builder.to_xml

The underscore may be used with any tag name, and the last underscore will just be removed.

Tag Attributes

Tag attributes may be supplied as method arguments. Here is our previous example, but using attributes rather than tags:

  @objects = [Object.new, Object.new, Object.new]

  builder = Nokogiri::XML::Builder.new do |xml|
    xml.root {
      xml.objects {
        @objects.each do |o|
          xml.object(:type => o.type, :class => o.class, :id => o.id)
        end
      }
    }
  end
  puts builder.to_xml

Tag Attribute Short Cuts

A couple attribute short cuts are available when building tags. The short cuts are available by special method calls when building a tag.

This example builds an “object” tag with the class attribute “classy” and the id of “thing”:

  builder = Nokogiri::XML::Builder.new do |xml|
    xml.root {
      xml.objects {
        xml.object.classy.thing!
      }
    }
  end
  puts builder.to_xml

All other options are still supported with this syntax, including blocks and extra tag attributes.

  Nokogiri::XML::Builder.new(:encoding => 'UTF-8') do |xml|
    ...
  end

# File lib/nokogiri/xml/builder.rb, line 128
      def initialize options = {}, &block
        namespace = self.class.name.split('::')
        namespace[-1] = 'Document'
        @doc      = eval(namespace.join('::')).new
        @parent   = @doc
        @context  = nil
        @arity    = nil

        options.each do |k,v|
          @doc.send(:"#{k}=", v)
        end

        return unless block_given?

        @arity = block.arity
        if @arity <= 0
          @context = eval('self', block.binding)
          instance_eval(&block)
        else
          yield self
        end

        @parent = @doc
      end

# File lib/nokogiri/xml/builder.rb, line 162
      def cdata string
        node = Nokogiri::XML::CDATA.new(@doc, string.to_s)
        insert(node)
      end

# File lib/nokogiri/xml/builder.rb, line 155
      def text string
        node = Nokogiri::XML::Text.new(string.to_s, @doc)
        insert(node)
      end

# File lib/nokogiri/xml/builder.rb, line 169
      def to_xml
        @doc.to_xml
      end

# File lib/nokogiri/xml/builder.rb, line 194
      def insert(node, &block)
        node.parent = @parent
        if block_given?
          @parent = node
          @arity ||= block.arity
          if @arity <= 0
            instance_eval(&block)
          else
            block.call(self)
          end
          @parent = node.parent
        end
        NodeBuilder.new(node, self)
      end