to_xml Doesn't Work on Objects Returned Through Rails ActiveRecord habtm Reference

Question

I have two rails active record classes, School and Instructor linked by a has_and_belongs_to_many relationship.

I need to query my instructors_controller for instruc

Answer 1

to_xml() tries to define a type attribute for each model attribute. For example, a User model with an age (INT) attribute will have: <age type="integer">42</age>. This type information is not encoded in JSON, which is why to_json() works for you. Add this method to your Instructor model:

def to_xml(options = {})
  to_xml_opts = {:skip_types => true} # no type information, not such a great idea!
  to_xml_opts.merge!(options.slice(:builder, :skip_instruct))
  # a builder instance is provided when to_xml is called on a collection of instructors,
  # in which case you would not want to have <?xml ...?> added to each item
  to_xml_opts[:root] ||= "instructor"
  self.attributes.to_xml(to_xml_opts)
end

This would however make your XML devoid of any type information - not good if someone has a JAVA REST client. A better strategy would be to filter self.attributes.slice(*keys).to_xml(to_xml_opts) where keys is an array of model attributes you want in the XML.