Added IgnoreUndeclared, an extension to silently ignore undeclared properties at hash intialization.

CHANGELOG.md

@@ -4,6 +4,7 @@
 * Removed support for Ruby 1.8.7 - [@dblock](https://github.com/dblock).
 * Ruby style now enforced with Rubocop - [@dblock](https://github.com/dblock).
 * [#138](https://github.com/intridea/hashie/pull/138): Added Hashie#Rash, a hash whose keys can be regular expressions or ranges - [@epitron](https://github.com/epitron).
+* [#131](https://github.com/intridea/hashie/pull/131): Added IgnoreUndeclared, an extension to silently ignore undeclared properties at intialization - [@righi](https://github.com/righi).
 * [#136](https://github.com/intridea/hashie/issues/136): Removed Hashie::Extensions::Structure - [@markiz](https://github.com/markiz).
 * [#107](https://github.com/intridea/hashie/pull/107): Fixed excessive value conversions, poor performance of deep merge in Hashie::Mash - [@davemitchell](https://github.com/dblock), [@dblock](https://github.com/dblock).
 * [#69](https://github.com/intridea/hashie/issues/69): Fixed assigning multiple properties in Hashie::Trash - [@einzige](https://github.com/einzige).

README.md

@@ -101,6 +101,32 @@ hash in question. This means you can safely merge together indifferent
 and non-indifferent hashes arbitrarily deeply without worrying about
 whether you'll be able to `hash[:other][:another]` properly.
 
+### IgnoreUndeclared
+
+This extension can be mixed in to silently ignore undeclared properties on
+initialization instead of raising an error. This is useful when using a
+Trash to capture a subset of a larger hash.
+
+```ruby
+class Person < Trash
+  include Hashie::Extensions::IgnoreUndeclared
+  property :first_name
+  property :last_name
+end
+
+user_data = {
+  first_name: 'Freddy',
+  last_name: 'Nostrils',
+  email: 'freddy@example.com'
+}
+
+p = Person.new(user_data) # 'email' is silently ignored
+
+p.first_name # => 'Freddy'
+p.last_name  # => 'Nostrils'
+p.email      # => NoMethodError
+```
+
 ### DeepMerge
 
 This extension allow you to easily include a recursive merging

lib/hashie.rb

@@ -12,6 +12,7 @@ module Hashie
     autoload :Coercion,          'hashie/extensions/coercion'
     autoload :DeepMerge,         'hashie/extensions/deep_merge'
     autoload :KeyConversion,     'hashie/extensions/key_conversion'
+    autoload :IgnoreUndeclared,  'hashie/extensions/ignore_undeclared'
     autoload :IndifferentAccess, 'hashie/extensions/indifferent_access'
     autoload :MergeInitializer,  'hashie/extensions/merge_initializer'
     autoload :MethodAccess,      'hashie/extensions/method_access'

lib/hashie/extensions/ignore_undeclared.rb

@@ -0,0 +1,41 @@
+module Hashie
+  module Extensions
+    # IgnoreUndeclared is a simple mixin that silently ignores
+    # undeclared properties on initialization instead of
+    # raising an error. This is useful when using a Trash to
+    # capture a subset of a larger hash.
+    #
+    # Note that attempting to retrieve an undeclared property
+    # will still raise a NoMethodError, even if a value for
+    # that property was provided at initialization.
+    #
+    # @example
+    #   class Person < Trash
+    #     include Hashie::Extensions::IgnoreUndeclared
+    #
+    #     property :first_name
+    #     property :last_name
+    #   end
+    #
+    #   user_data = {
+    #      :first_name => 'Freddy',
+    #      :last_name => 'Nostrils',
+    #      :email => 'freddy@example.com'
+    #   }
+    #
+    #   p = Person.new(user_data) # 'email' is silently ignored
+    #
+    #   p.first_name # => 'Freddy'
+    #   p.last_name  # => 'Nostrils'
+    #   p.email      # => NoMethodError
+    module IgnoreUndeclared
+      def initialize_attributes(attributes)
+        attributes.each_pair do |att, value|
+          if self.class.property?(att) || (self.class.respond_to?(:translations) && self.class.translations.include?(att.to_sym))
+            self[att] = value
+          end
+        end if attributes
+      end
+    end
+  end
+end

spec/hashie/extensions/ignore_undeclared_spec.rb

@@ -0,0 +1,23 @@
+require 'spec_helper'
+
+describe Hashie::Extensions::IgnoreUndeclared do
+  class ForgivingTrash < Hashie::Trash
+    include Hashie::Extensions::IgnoreUndeclared
+    property :city
+    property :state, from: :provence
+  end
+
+  subject { ForgivingTrash }
+
+  it 'should silently ignore undeclared properties on initialization' do
+    expect { subject.new(city: 'Toronto', provence: 'ON', country: 'Canada') }.to_not raise_error
+  end
+
+  it 'should work with translated properties (with symbol keys)' do
+    expect(subject.new(provence: 'Ontario').state).to eq('Ontario')
+  end
+
+  it 'should work with translated properties (with string keys)' do
+    expect(subject.new(provence: 'Ontario').state).to eq('Ontario')
+  end
+end