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Using YAML as a parameter hash in Ruby

Posted August 11th, 2009 at 2:04 pm

Sometimes while coding Ruby applications the need develops to have some sort of metadata available as a configuration file. I have written some Ruby code that allows parameters that exist in a yaml file to be used as though they are in the class itself. In addition, I required code that allows the class to modify these parameters and then save them back to the file. Ruby's method_missing is a major player here. Anyway, I thought I would share this code.

To give an example of what exactly this does, assume that there exists a file called 'config.yml' that contains some key value pair such as :name => 'Bob':

  1. --- 
  2. :name: Bob

Using this class, we could do stuff like:

  1. require 'boilerplate'
  2.  
  3. class Test < Boilerplate
  4.   def run
  5.     puts "Name is: #{name}"
  6.     super
  7.   end
  8. end
  9.  
  10. t = Test.new
  11. puts t.name       #=> 'Bob'
  12. t.name = 'Joe'
  13. puts t.name       #=> 'Joe'
  14. t.run             #=> 'Name is: Joe'

Which would result in the yaml file now having the key value pair of :name => 'Joe'. If you didn't want to call 'run' you could call flush manually or add it as a call to some other method.

Here is the boilerplate.rb code in full:

  1. class Boilerplate
  2.   require 'yaml'
  3.   require 'ftools'
  4.  
  5.   CACHE_LOCATION  = File.join('.')
  6.   CACHE_FILE      = 'config.yml'
  7.   CACHE_PATH      = File.join(File.expand_path(CACHE_LOCATION), CACHE_FILE)
  8.  
  9.   def initialize
  10.     ensure_cache_exists
  11.     load_settings
  12.   end
  13.  
  14.   def run
  15.     # do stuff here
  16.     flush
  17.   end
  18.  
  19.   private
  20.  
  21.   def method_missing(symbol, *args, &block)
  22.     string = symbol.to_s # need for '=' method
  23.  
  24.     if @options.key?(symbol)
  25.       @options[symbol]
  26.     elsif string.index('=') + 1 == string.length && @options.key?(string.gsub('=', '').intern)
  27.       @options[string.gsub('=', '').intern] = *args
  28.     else
  29.       super(symbol, *args, &block)
  30.     end
  31.   end
  32.  
  33.   def load_settings
  34.     @options = {}
  35.     imports = YAML.load_file(CACHE_PATH)
  36.     if imports
  37.       imports.each_pair do |key, value|
  38.         if not key.is_a? Symbol
  39.           imports[key.to_sym] = value
  40.           imports.delete(key)
  41.         end
  42.       end
  43.  
  44.       @options = imports.merge(@options)
  45.       end
  46.     end
  47.  
  48.   def ensure_cache_exists
  49.     File.makedirs(CACHE_LOCATION)
  50.     File.new(CACHE_PATH, 'a+') unless File.exists?(CACHE_PATH) 
  51.   end
  52.  
  53.   def flush
  54.     File.open(CACHE_PATH, 'w') do |f|
  55.       f.puts(YAML::dump(@options))
  56.     end
  57.   end
  58. end