How can I insert a tree of nodes with namespaces into an existing XML file using Nokogiri?

Question

I've been using Nokogiri to generate an XML file (specifically, a GraphML document using some yEd namespaces). An example of the type of file I'm generating:



  
  
  
  
  
  
  
    
    
      
      
        
          
          
          
          DAY
          
        
      
    
    
      
      
        
          
          
          
          STL
          
        
      
    
    
      
      
        
          
          
          
          DFW
          
        
      
    
    
      
      
        
          
          
          American Airlines
        
      
    
    
      
      
        
          
          
          American Airlines
        
      
    
    
      
      
        
          
          
          American Airlines

The document has a basic structure that doesn't change from document to document, and then a collection of and tags specific to each document.

I've been able to successfully build this XML in a single method using Nokogiri::XML::Builder.

However, I now want to generate this file based on a different type of data as well -- most of the file will be unchanged; only my code that loops over data and generates the and tags will change. So I'm effectively trying to create an XML template that I can call from multiple Ruby methods, which will then insert their own variants.

My thought was that I could save an XML file with everything except the and tags. I would then have each different method use Nokogiri::XML::Builder to create a DocumentFragment of and tags, open the template file, and insert the DocumentFragment in as a child of the tag:

YED_TEMPLATE = "#{Rails.root}/app/views/xml_templates/flights.yed.graphml"

def self.yed_from_string(flight_string)
  airports = flight_string.split(/[,-]/).tally

  output = File.open(YED_TEMPLATE) {|f| Nokogiri::XML(f)}

  nodes = Nokogiri::XML::DocumentFragment.parse("")
  Nokogiri::XML::Builder.with(nodes) do |xml|
    airports.map{|airport, visits| yed_airport_node(xml, airport, airport, visits)}
  end

  # Write similar code for edges

  output.at("graph").add_child(nodes)
  return output.to_xml
end

private

def self.yed_airport_node(xml, id, text, visits)
  xml.node(id: "n#{id}") do
    xml.data(key: "d5")
    xml.data(key: "d6") do
      xml[:y].ShapeNode do
        xml[:y].Geometry(circle_size(visits))
        xml[:y].Fill(color: BASE_STYLES[:node_color_fill], transparent: false)
        xml[:y].BorderStyle(color: BASE_STYLES[:node_color_border], raised: false, type: "line", width: BASE_STYLES[:node_width_border])
        xml[:y].NodeLabel(text, **font(visits))
        xml[:y].Shape(type: "ellipse")
      end
    end
  end
  return nil
end

# Write similar method for edges

So this code largely does what I want it to. It successfully loads the template XML file at YED_TEMPLATE, it successfully creates a DocumentFragment, and it successfully inserts the DocumentFragment into the template XML...

...as long as I don't include the y namespace tags (y:ShapeNode, y:Geometry, etc.). If I do, I get an ArgumentError (Namespace y has not been defined).

That makes sense to me, since the DocumentFragment isn't aware of all of the namespace definitions in the template XML file. But I have no idea how to actually provide the namespaces to a DocumentFragment, since it doesn't have a true root tag to add them to; the real root is in the template file.

Is there a way for me to pass namespace definitions into a Nokogiri::XML::Builder for a DocumentFragment? Alternatively, is there a better way for me to create a collection of nested tags with namespaces, and insert them into an existing XML document?

max · Accepted Answer

A nifty little tick if you want to create a builder instance scoped to a namespace is to use Nokogiri::XML::Builder.with(doc.root):

doc = Nokogiri::XML('
')
builder = Nokogiri::XML::Builder.with(doc.root) do |xml|
  xml['y'].Shapenode do |sn|
    sn.Foo
    sn.Bar
  end
end

builder.to_xml outputs:

Worth noting though is that it mutates doc. If I where to do this I would use Nokogiri::XML::Builder.with(doc.root.dup) which prevents it from mutating the arguments.

You can also just create builders with any arbitrary root with:

builder = Nokogiri::XML::Builder.new do |xml|
  xml.root('xmlns:y' => 'bar') do
    xml['y'].Shapenode
  end
end

builder.doc.xpath('/*').children will slice out the node set.

How can I insert a tree of nodes with namespaces into an existing XML file using Nokogiri?

Answers (1)

Related Questions