Refactor Attribute Tracking Code

Gemfile

@@ -9,7 +9,7 @@ group :test do
   gem 'rspec', '~> 3.0.0'
   gem 'cucumber'
   gem 'simplecov', require: false
-  gem 'coveralls', require: false
+  gem 'coveralls', require: false if RUBY_VERSION > '1.9.3'
 
   if ENV["NEW_RAILS"]
     gem 'activemodel'

lib/aws-record.rb

@@ -22,7 +22,10 @@ module Record
     autoload :DirtyTracking,    'aws-record/record/dirty_tracking'
     autoload :Errors,           'aws-record/record/errors'
     autoload :ItemCollection,   'aws-record/record/item_collection'
+    autoload :ItemData,         'aws-record/record/item_data'
     autoload :ItemOperations,   'aws-record/record/item_operations'
+    autoload :KeyAttributes,    'aws-record/record/key_attributes'
+    autoload :ModelAttributes,  'aws-record/record/model_attributes'
     autoload :Query,            'aws-record/record/query'
     autoload :SecondaryIndexes, 'aws-record/record/secondary_indexes'
     autoload :TableMigration,   'aws-record/record/table_migration'

lib/aws-record/record.rb

@@ -204,6 +204,12 @@ def mutation_tracking_enabled?
         @track_mutations == false ? false : true
       end
 
+      def model_valid?
+        if @keys.hash_key.nil?
+          raise Errors::InvalidModel.new("Table models must include a hash key")
+        end
+      end
+
       private
       def _user_agent(custom)
         if custom

lib/aws-record/record/attribute.rb

@@ -39,11 +39,6 @@ class Attribute
       #   "M", "L". Optional if this attribute will never be used for a key or
       #   secondary index, but most convenience methods for setting attributes
       #   will provide this.
-      # @option options [Boolean] :mutation_tracking Optional attribute used to
-      #   indicate whether mutations to values should be explicitly tracked when
-      #   determining if a value is "dirty". Important for collection types
-      #   which are often primarily modified by mutation of a single object
-      #   reference. By default, is false.
       # @option options [Boolean] :persist_nil Optional attribute used to
       #   indicate whether nil values should be persisted. If true, explicitly
       #   set nil values will be saved to DynamoDB as a "null" type. If false,
@@ -56,7 +51,6 @@ def initialize(name, options = {})
         @database_name = options[:database_attribute_name] || name.to_s
         @dynamodb_type = options[:dynamodb_type]
         @marshaler = options[:marshaler] || DefaultMarshaler
-        @mutation_tracking = options[:mutation_tracking]
         @persist_nil = options[:persist_nil]
         dv = options[:default_value]
         @default_value = type_cast(dv) unless dv.nil?
@@ -85,12 +79,6 @@ def serialize(raw_value)
         @marshaler.serialize(cast_value)
       end
 
-      # @return [Boolean] true if this attribute should do active mutation
-      #  tracking, false otherwise. Default: false
-      def track_mutations?
-        @mutation_tracking ? true : false
-      end
-
       # @return [Boolean] true if this attribute will actively persist nil
       #   values, false otherwise. Default: false
       def persist_nil?