Array to_xml


Why is it that…


myarray = [“one”]
=> [“one”]

RuntimeError: Not all elements respond to to_xml
from /foo/vendor/rails/activerecord/lib/…/…/activesupport/lib/
active_support/core_ext/array/conversions.rb:62:in `to_xml’
from (irb):94


… however …


myarray2 = [{:one => “onevalue”}]
=> [{:one=>“onevalue”}]

=> "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<records type="array
“>\n \n onevalue\n \n\n”


Is there a way I can convert an array to xml without having to wrap
each element in a hash???


What do you want the resulting XML to look like? Usually XML has name/
value format.

You can do this:

class Symbol
def to_xml
{self => self.to_s}.to_xml

and then you can call :hello.to_xml

=> hello

That’s a little dangerous, though, and it may turn out that you should
rethink the XML schema, and use hashes in general.


On 7 Oct 2008, at 02:30, Sam wrote:

from (irb):94
“>\n \n onevalue\n \n\n”

In a nutshell, strings don’t have a to_xml method, but hashes do.


Is there a way I can convert an array to xml without having to wrap
each element in a hash???

What do you want the output to look like ?



The standard thing to do is put classes in there instead of strings,
so each error would be an instance of class Error, which would respond
to to_xml with foo or whatever. See, for example, Pat
Maddox’s Blog:

If you are worried about reversibility, you can change active_support
\core_ext\array\conversions so that the to_xml method looks like this
at the top:

      options[:root]     ||= all? { |e| e.is_a?(first.class) &&

first.class.to_s != “Hash” } ? first.class.to_s.underscore.pluralize :
map!{|e| ( == “String”) ? {options[:root].to_sym
=> e} : e}

      raise "Not all elements respond to to_xml" unless all? { |e|

e.respond_to? :to_xml }

      options[:children] ||= options[:root].singularize
      options[:indent]   ||= 2
      options[:builder]  ||= =>


The XML you get back isn’t pretty, but it doesn’t crash:

<?xml version=\"1.0\" encoding=\"UTF-8\"?> foo bar

Cleaning it up more than this might be a bit tricky. If this is
something a lot of people would like, I’d look at it some more, but I
think it’s pretty unusual, and it’s usually easier to use objects.



I’m wanting something like…

foo bar

I find it really interesting that a Rails controller will accept xml

one two

… and transform it into a hash…

{ :process_codes => { :code => [ “one”, “two” ] } }

… but will not go back the other way when I want to convey errors…

{ :errors => { :error => [ “foo”, “bar” ] } }


Thanks Michael.

I’ve taken the easy (and hacky) way out by using an
ActiveRecord::Errors object which is transformed implements to_xml
quite nicely.
The hacky bit is that I’m not always adding an error that coincides
with an attribute of the model I’m exploiting … eg,

errors.add( :code, “#{code} is not found” )

…when my model object doesn’t actually have a “code” attribute.
Also… under some scenarios I may not have a model instance at all
but need to create one in order to gain access to the to_xml friendly
Errors object by doing something like…

errors =

… which is of course hacky, but more readily thrown together than
implementing a custom errors class or modifying the conversions.rb
The Errors object is also nice because it allows multiple errors with
the same key…

errors.add( :code, “#{code} is not found” )
errors.add( :code, “#{code} has already been processed” )