has_one example

entity.rb

require 'byebug'

module AutotaskAPI
  class Entity
    class_attribute :fields, :client, :find_cache
    attr_accessor :attributes, :raw_xml

    def initialize(xml)
      self.raw_xml = xml
      self.attributes = {}
      fields.each do |field|
        attributes[field] = xml.at_xpath("Autotask:#{field.to_s == 'id' ? 'id' : field.to_s.camelize.gsub(/Id$/, 'ID')}",
          Autotask: Client::NAMESPACE).text.strip rescue ''
      end
      attributes
    end

    def method_missing(method, *args, &block)
      if attributes.include?(method.to_sym)
        attributes[method.to_sym]
      else
        super
      end
    end

    def self.find(id, field = nil)
      raise "No initialized client!" unless client
      self.find_cache ||= {}

      query = AutotaskAPI::QueryXML.new do |query|
        query.entity = self.to_s.demodulize
        query.field = (field || 'id')
        query.expression = id
      end
      find_cache[id] ||= client.entities_for(query).first
    end

    def self.belongs_to(name, options = {})
      name = name.to_s
      klass = "AutotaskAPI::#{(options[:class_name] || name).to_s.classify}".constantize
      foreign_key = name.foreign_key
      define_method name do
        klass.find send(foreign_key)
      end
    end

    def self.has_one(name, options = {})
      name = name.to_s
      klass = "AutotaskAPI::#{(name).to_s.classify}".constantize
      define_method name do
        klass.find(self.id, options[:foreign_key])
      end
    end
  end
end

The has_one example works OK, but is there a better way of doing this? I had to remove the send() as I couldn't make it work.

service_call.rb
has_one :service_call_ticket, foreign_key: :ServiceCallID