model_xml is a small gem which helps in the conversion of ruby objects to xml. It is designed with ActiveRecord objects in mind, but should work with any Ruby object.

gem 'model_xml' in your gemfile, or gem install model_xml

If you are using Rails, just require model_xml any time after ActiveRecord has loaded - the bottom of your environment.rb file is fine. Otherwise, require model_xml, then include ModelXML in your object.

Take a look at ActiveRecord's baked in to_xml method first. If it meets your requirements, obviously just use that. If not, read on.

The simplest usage method is just to declare the list of fields you want in your model's xml representation, like this:

class User < ActiveRecord::Base
  model_xml :first_name, :last_name, :dob
end

Then user.to_xml gives:

<user>
  <first_name>John</first_name>
  <last_name>Jones</last_name>
  <dob>1970-12-23</dob>
</user>

Just like ActiveRecord's to_xml method, the :only, :except, and :skip_instruct options are supported.

Note that (unlike ActiveRecords's to_xml) the field names can be any method in your object, not just database columns - eg

class User < ActiveRecord::Base
  model_xml :full_name, :dob

  def full_name
    "#{first_name} #{last_name}"
  end
end

behaves as expected:

<user>
  <full_name>John Jones</full_name>
  <dob>1970-12-23</dob>
</user>

You can even declare a formatting proc on the fly, like this:

class User < ActiveRecord::Base
  model_xml [:full_name, proc {|u| "#{u.first_name} #{u.last_name}"], :dob
end

which would give the same result.

For more complicated setups, you can use block notation like this:

class User < ActiveRecord::Base
  model_xml do
    full_name proc {|u| "#{u.first_name} #{u.last_name}"}
    dob
    password
    last_logged_in
  end
end

The above relies on method_missing to work - so note that if you are using a ruby reserved method name (like id) for your tag, you may need to use the longer form block notation with the field operator:

class User < ActiveRecord::Base
  model_xml do
    field :id, proc {|u| u.some_other_id_method}
  end
end

For conditional data sets, you can declare named blocks using block notation like this:

class User < ActiveRecord::Base
  model_xml :first_name, :last_name
  model_xml :personal_details do
    dob
    password
    last_logged_in
  end
end

By default named blocks are excluded from the xml, so user.to_xml gives

<user>
  <first_name>John</first_name>
  <last_name>Jones</last_name>
</user>

but can be included explicitly - so user.to_xml(:personal_details => true) gives

<user>
  <first_name>John</first_name>
  <last_name>Jones</last_name>
  <dob>1970-12-23</dob>
  <password>foo</password>
  <last_logged_in>2012-04-10</last_logged_in>
</user>

Finally, if any of the field names return objects which themselves respond to to_xml, then their xml representations will be embedded. So if you use the name of an active record association, then the child(ren) should be embedded in the xml as you'd expect.

Source is on github https://github.com/rob-anderson/model_xml

Send bugs or comments to me rob.anderson@paymentcardsolutions.co.uk