Hey all,
I've been spending some time trying to figure out the best way to
create some XML output while mixing in ActiveRecord serialization.
After looking through the source for the XmlMarkup, XmlBase, and
ActiveRecord::XmlSerializer (in Rails 2. I also looked at Rails 3 and
the code seems to be largely in ActiveModel) classes, the best I could
find was using the "tag!" method to output the attributes/methods of
an ActiveRecord object individually. Since I wanted to have all of
the goodness of just specifying an array of attributes/methods/procs I
ended up coding my own monkey patch (see below), but I'd love it if
this sort of functionality was part of Rails so that my monkey patch
doesn't break and so that anybody could use it. If there's no better
solution currently implemented, I'd be happy to spend some time
working on the project. I just thought I'd check in with ya'll
first 
So the behavior I want would look something like this (as an sample post.xml.builder view):
xml.instruct! xml.active_record_model_tag!(@post, :attributes => [:id, :body, :updated_at]) do xml.active_record_model_tag!(@post.author) @post.comments.each do |comment| xml.active_record_model_tag!(comment, :attributes => [:id, :body, :created_at], :methods => [:up_vote_percentage]) end end
I also like this solution because, while I've been using "to_xml" for a long time and while I really like it, I think it starts to get unreasonably complex when I'm using the :only key in the options to display attributes in subsequent associations of the main object (the author and comments associations off of the @post main object in the example above) and you may get name conflicts where maybe you wanted the "created_at" for just the comments and not the post.
I've written the (incomplete but sufficient for my needs) monkey patch below to address the issue, but again, I'd love for this to be built into Rails and for it to use the ActiveModel serialization. If it needs to be implemented, my main question is: should this be continue to be a monkey patch of Builder which is defined by Rails, or would it be best to find some way to implement it via Builder and utilize in Rails?
module Builder class XmlMarkup < XmlBase def active_record_model_tag!(model_object, options = {}) undefined_keys = options.keys.collect(&:to_sym) - [:attributes, :methods] raise ArgumentError, "Undefined keys: #{undefined_keys.to_sentence}" unless undefined_keys.empty?
model_class = model_object.class
attributes = options[:attributes] || model_class.column_names methods = options[:methods] ||
self.tag!(model_class.to_s.tableize.singularize) do attributes.each do |attribute| value = model_object.send(attribute) type = model_class.columns_hash[attribute.to_s].type
properties = {} properties = properties.merge(:type => type) if type properties = properties.merge(:nil => true) if value.nil? self.tag!(attribute, value, properties) end
methods.each do |method| value = model_object.send(method)
properties = properties.merge(:nil => true) if value.nil? self.tag!(method, value, properties) end
yield if block_given? end end end end