Module: UsingYAML::ClassMethods

Defined in:
lib/using_yaml.rb

Instance Method Summary collapse

Instance Method Details

#using_yaml(*args) ⇒ Object

Used to configure UsingYAML for a class by defining what files should be loaded and from where.

include UsingYAML
using_yaml :foo, :bar, :path => "/some/where"

args can contain either filenames or a hash which specifices a path which contains the corresponding files.

The value of :path must either be a string or Proc (see using_yaml_path for more information on overriding paths).



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# File 'lib/using_yaml.rb', line 100

def using_yaml(*args)
  # Include the instance methods which provide accessors and
  # mutators for reading/writing from/to the YAML objects.
  include InstanceMethods

  # Each argument is either a filename or a :path option
  args.each do |arg|
    case arg
    when Symbol, String
      # Define accessors for this file
      using_yaml_file(arg.to_s)
    when Hash
      # Currently only accepts { :path => ... }
      next unless arg.size == 1 && arg.keys.first == :path
      
      # Take note of the path
      UsingYAML.path = [self.inspect, arg.values.first]
    end
  end
end

#using_yaml_file(filename) ⇒ Object

Special attr_accessor for the suppiled filename such that files are intelligently loaded/written to disk.

using_yaml_file(:foo) # => attr_accessor(:foo) + some magic

If class Example is setup with the above, then:

example = Example.new
example.foo      # => loads from foo.yml
example.foo.bar  # => equivalent to example.foo['bar']
example.foo.save # => serialises to foo.yml



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# File 'lib/using_yaml.rb', line 133

def using_yaml_file(filename)
  # Define an reader for filename such that the corresponding
  # YAML file is loaded. Example: using_yaml_file(:foo) will look
  # for foo.yml in the specified path.
  define_method(filename) do
    # Work out the absolute path for the filename and get a handle
    # on the cachestore for that file.
    pathname = using_yaml_path.join("#{filename}.yml").expand_path
    yaml     = (@using_yaml_cache ||= {})[pathname]

    # If the yaml exists in our cache, then we don't need to hit
    # the disk.
    return yaml if @using_yaml_cache.has_key? pathname

    # Safe disk read which either reads and parses a YAML object
    # (and caches it against future reads) or graciously ignores
    # the file's existence. Note that an error will appear on
    # stderr to avoid typos (or similar) from causing unexpected
    # behavior. See +UsingYAML.squelch!+ if you wish to hide the
    # error.
    begin
      @using_yaml_cache[pathname] = UsingYAML.add_extensions(YAML.load_file(pathname), pathname)
    rescue Exception => e
      $stderr.puts "(UsingYAML) Could not load #{filename}: #{e.message}" unless UsingYAML.squelched?
      @using_yaml_cache[pathname] = UsingYAML.add_extensions(nil, pathname)
    end
  end

  # Define a writer for filename such that the incoming object is
  # treated as a UsingYAML-ized Hash (magical properties). Be
  # aware that the incoming object will not be saved to disk
  # unless you explicitly do so.
  define_method("#{filename}=".to_sym) do |object|
    # Work out the absolute path for the filename and get a handle
    # on the cachestore for that file.
    pathname = using_yaml_path.join("#{filename}.yml").expand_path
    (@using_yaml_cache ||= {})[pathname] = UsingYAML.add_extensions(object, pathname)
  end
end