Rails 2: #to_xml(:methods => :method_name) when #method_name returns an Array

Question

Is it possible to override how #to_xml renders a method result if it's an Array?

Given #numbers is not a field but a method And @object.numbers #=> [0,1,2,3,4,5]

currently it does:

@object.to_xml(:methods => :numbers)
=> "<object><numbers>012345</numbers></object>"

is it possible to override this behavior so it returns:

@object.to_xml(:methods => :numbers)
=> "<object>
      <numbers>
        <number>0</number>
        <number>1</number>
        <number>2</number>
        <number>3</number>
        <number>4</number>
        <number>5</number>
      </numbers>
    </object>"

(formatted so it's easily read)

Thanks in advance for your suggestions!

Answer 1

You have two options:

1. Upgrade to Rails 3. It already has the desired output.

   gem "activemodel", '~> 3.2.12'
   require "active_model"
   
   # This could be an Active Record model
   class Result
     include ActiveModel::Serializers::Xml
   
     def numbers
       (0..5).to_a
     end
   
     def attributes
       {}
     end
   end
   
   result = Result.new
   puts result.to_xml(:methods => :numbers)
   

   Outputs:

   <?xml version="1.0" encoding="UTF-8"?>
   <result>
     <numbers type="array">
       <number type="integer">0</number>
       <number type="integer">1</number>
       <number type="integer">2</number>
       <number type="integer">3</number>
       <number type="integer">4</number>
       <number type="integer">5</number>
     </numbers>
   </result>
   

2. Use XML Builder where you are in full control of the output. You will have to specify all attributes manually.

   # app/views/results/show.xml.builder
   xml.instruct!
   xml.result {
     xml.numbers {
       result.numbers.each do |n|
         xml.number n
       end
     }
   }
   

   Outputs:

   <?xml version="1.0" encoding="UTF-8"?>
   <result>
     <numbers>
       <number>0</number>
       <number>1</number>
       <number>2</number>
       <number>3</number>
       <number>4</number>
       <number>5</number>
     </numbers>
   </result>
   

Answer 2

You can use the :procs option to add a custom rendering for your method inside the model:

def to_xml(options={})
  numbers_proc = Proc.new do |options|
    xml = options[:builder]
    xml.numbers do
      numbers.each do |n|
        xml.number n
      end
    end
  end
  super options.merge(:procs => numbers_proc)
end