Loading .yml configuration data with the code from http://speakmy.name/2011/05/29/simple-configuration-for-ruby-apps

app_data.rb

module AppData

#require 'deep_symbolizable'

  # again - it's a singleton, thus implemented as a self-extended module
  extend self

  @_settings = {}
  attr_reader :_settings

  # This is the main point of entry - we call Settings.load! and provide
  # a name of the file to read as it's argument. We can also pass in some
  # options, but at the moment it's being used to allow per-environment
  # overrides in Rails
  def load!(filename, options = {})
    newsets = YAML::load_file(filename).deep_symbolize
    newsets = newsets[options[:env].to_sym] if \
                                               options[:env] && \
                                               newsets[options[:env].to_sym]
    deep_merge!(@_settings, newsets)
  end

  # Deep merging of hashes
  # deep_merge by Stefan Rusterholz, see http://www.ruby-forum.com/topic/142809
  def deep_merge!(target, data)
    merger = proc{|key, v1, v2|
      Hash === v1 && Hash === v2 ? v1.merge(v2, &merger) : v2 }
    target.merge! data, &merger
  end

  def method_missing(name, *args, &block)
    @_settings[name.to_sym] ||
    fail(NoMethodError, "unknown configuration root #{name}", caller)
  end

end

deep_symbolizable.rb

# Symbolizes all of hash's keys and subkeys.
# Also allows for custom pre-processing of keys (e.g. downcasing, etc)
# if the block is given:
#
# somehash.deep_symbolize { |key| key.downcase }
#
# Usage: either include it into global Hash class to make it available to
# to all hashes, or extend only your own hash objects with this
# module.
# E.g.:
# 1) class Hash; include DeepSymbolizable; end
# 2) myhash.extend DeepSymbolizable

module DeepSymbolizable

  class Hash
    include DeepSymbolizable
  end
  
  def deep_symbolize(&block)
    method = self.class.to_s.downcase.to_sym
    syms = DeepSymbolizable::Symbolizers
    syms.respond_to?(method) ? syms.send(method, self, &block) : self
  end

  module Symbolizers
    extend self

    # the primary method - symbolizes keys of the given hash,
    # preprocessing them with a block if one was given, and recursively
    # going into all nested enumerables
    def hash(hash, &block)
      hash.inject({}) do |result, (key, value)|
        # Recursively deep-symbolize subhashes
        value = _recurse_(value, &block)

        # Pre-process the key with a block if it was given
        key = yield key if block_given?
        # Symbolize the key string if it responds to to_sym
        sym_key = key.to_sym rescue key

        # write it back into the result and return the updated hash
        result[sym_key] = value
        result
      end
    end

    # walking over arrays and symbolizing all nested elements
    def array(ary, &block)
      ary.map { |v| _recurse_(v, &block) }
    end

    # handling recursion - any Enumerable elements (except String)
    # is being extended with the module, and then symbolized
    def _recurse_(value, &block)
      if value.is_a?(Enumerable) && !value.is_a?(String)
        # support for a use case without extended core Hash
        value.extend DeepSymbolizable unless value.class.include?(DeepSymbolizable)
        value = value.deep_symbolize(&block)
      end
      value
    end
  end

end

rails console output

marks-imac:lib railsdev$ pwd
/Users/railsdev/Development/railsprojects/Learning/Marks-Attempts/Test-Area/bootstrap-dropdown-buttons/lib
marks-imac:lib railsdev$ cd generic_search/
marks-imac:generic_search railsdev$ rails c
Loading development environment (Rails 3.2.5)
1.9.3-p125 :001 > AppData.load!("#{Rails.root}/config/initializers/search_configurations.yml")
NameError: uninitialized constant AppData
	from (irb):1
	from /Users/railsdev/.rvm/gems/ruby-1.9.3-p125@bootstrap-dropdown-buttons/gems/railties-3.2.5/lib/rails/commands/console.rb:47:in `start'
	from /Users/railsdev/.rvm/gems/ruby-1.9.3-p125@bootstrap-dropdown-buttons/gems/railties-3.2.5/lib/rails/commands/console.rb:8:in `start'
	from /Users/railsdev/.rvm/gems/ruby-1.9.3-p125@bootstrap-dropdown-buttons/gems/railties-3.2.5/lib/rails/commands.rb:41:in `<top (required)>'
	from script/rails:6:in `require'
	from script/rails:6:in `<main>'
1.9.3-p125 :002 > GenericSearch::AppData.load!("#{Rails.root}/config/initializers/search_configurations.yml")
LoadError: Expected /Users/railsdev/Development/railsprojects/Learning/Marks-Attempts/Test-Area/bootstrap-dropdown-buttons/lib/generic_search/app_data.rb to define GenericSearch::AppData
	from /Users/railsdev/.rvm/gems/ruby-1.9.3-p125@bootstrap-dropdown-buttons/gems/activesupport-3.2.5/lib/active_support/dependencies.rb:503:in `load_missing_constant'
	from /Users/railsdev/.rvm/gems/ruby-1.9.3-p125@bootstrap-dropdown-buttons/gems/activesupport-3.2.5/lib/active_support/dependencies.rb:192:in `block in const_missing'
	from /Users/railsdev/.rvm/gems/ruby-1.9.3-p125@bootstrap-dropdown-buttons/gems/activesupport-3.2.5/lib/active_support/dependencies.rb:190:in `each'
	from /Users/railsdev/.rvm/gems/ruby-1.9.3-p125@bootstrap-dropdown-buttons/gems/activesupport-3.2.5/lib/active_support/dependencies.rb:190:in `const_missing'
	from (irb):2
	from /Users/railsdev/.rvm/gems/ruby-1.9.3-p125@bootstrap-dropdown-buttons/gems/railties-3.2.5/lib/rails/commands/console.rb:47:in `start'
	from /Users/railsdev/.rvm/gems/ruby-1.9.3-p125@bootstrap-dropdown-buttons/gems/railties-3.2.5/lib/rails/commands/console.rb:8:in `start'
	from /Users/railsdev/.rvm/gems/ruby-1.9.3-p125@bootstrap-dropdown-buttons/gems/railties-3.2.5/lib/rails/commands.rb:41:in `<top (required)>'
	from script/rails:6:in `require'
	from script/rails:6:in `<main>'
1.9.3-p125 :003 > GenericSearch
 => GenericSearch 
1.9.3-p125 :004 > AppData.load!("#{Rails.root}/config/initializers/search_configurations.yml")
NoMethodError: undefined method `deep_symbolize' for #<Hash:0x007fe146e2abd8>
	from /Users/railsdev/Development/railsprojects/Learning/Marks-Attempts/Test-Area/bootstrap-dropdown-buttons/lib/generic_search/app_data.rb:16:in `load!'
	from (irb):4
	from /Users/railsdev/.rvm/gems/ruby-1.9.3-p125@bootstrap-dropdown-buttons/gems/railties-3.2.5/lib/rails/commands/console.rb:47:in `start'
	from /Users/railsdev/.rvm/gems/ruby-1.9.3-p125@bootstrap-dropdown-buttons/gems/railties-3.2.5/lib/rails/commands/console.rb:8:in `start'
	from /Users/railsdev/.rvm/gems/ruby-1.9.3-p125@bootstrap-dropdown-buttons/gems/railties-3.2.5/lib/rails/commands.rb:41:in `<top (required)>'
	from script/rails:6:in `require'
	from script/rails:6:in `<main>'
1.9.3-p125 :005 > 

search_configurations.yml

# Search Conditions
#   manually configured
#
#   EDIT with CARE
#   
generic_conditions:
 - contains
 - equals
 - 'starts with'
 - 'ends with'
 - 'from/to'
 - 'matches'

models:
  diagnosis:
    fields: 
     - code
     - description
    conditions: 
      - contains
      - equals
      - 'starts with'
      - 'ends with'
      - 'from/to'
      - 'matches'
  services:
    fields: 
      code:
       - contains
       - equals
       - 'starts with'
       - 'ends with'
       - matches
      description:
       - 'valid from'

emails:
  admin:    someadmin@somewhere.net
  support:  support@somewhere.net

urls:
  search:   http://google.com
  blog:     http://speakmy.name

File locations

lib/generic_search/app_data.rb
config/initializers/deep_symbolizable.rb
config/initializers/search_configurations.yml

Was this the correct place to put the class override?

module DeepSymbolizable

class Hash
include DeepSymbolizable
end

def deep_symbolize(&block)
method = self.class.to_s.downcase.to_sym
syms = DeepSymbolizable::Symbolizers
syms.respond_to?(method) ? syms.send(method, self, &block) : self
end

you can just do the inclusion at the end of deep_symbolizable.rb, like here: https://gist.github.com/3706140

File locations in this case can be like this:

config/initializers/01_deep_symbolizable.rb
config/initializers/99_app_data.rb
config/data/search_configurations.yml

If will auto-load and execute deep_symbolizable.rb first, then app_data.rb - after that you can load your yml files. As app_data.rb is executed at the end - you can even load your data at the end of that file, as Hash should already be set up by that time