Working implementation with specs.

lib/data_patcher.rb

@@ -0,0 +1,32 @@
+require 'activesupport'
+
+class DataPatcher
+
+  def analyze_record(key, attributes)
+    existing = Item.find_by_asin(attributes[key])
+    if existing
+      existing_attributes = existing.attributes.dup.symbolize_keys.except(:id)
+      diff = attributes.diff(existing_attributes)
+      # always include the key in the mix so that a look-up is possible when applying the patch
+      unless diff.empty?
+        patch[:modified] ||= []
+        diff[key] = attributes[key]
+        patch[:modified] << diff
+      end
+    else
+      patch[:added] ||= []
+      patch[:added] << attributes
+    end
+  end
+
+  # test commodity - remove ?
+  def analyze_records(key, records)
+    records.each { |record| analyze_record(key, record) }
+  end
+
+  def patch
+    @patch ||= {}
+  end
+
+end
+

spec/data_patcher_spec.rb

@@ -1,7 +1,44 @@
 require File.dirname(__FILE__) + '/spec_helper'
 
-describe "DataPatcher" do
-  it "fails" do
-    fail "hey buddy, you should probably rename this file and start specing for real"
+describe DataPatcher do
+
+  before(:each) do
+    @existing_item_1 = {
+                :title => "Mastering Data Warehouse Aggregates",
+                :summary => "The first book to provide in-depth coverage of star schema aggregates...",
+                :asin => "0471777099" }
+    @existing_item_2 = {
+                  :title => "The Data Warehouse ETL Toolkit",
+                  :summary => "The single most authoritative guide on the most difficult phase of building a data warehouse",
+                  :asin => "0764567578" }
+    @existing_items = [@existing_item_1, @existing_item_2]
+    Item.delete_all
+    Item.create!(@existing_item_1)
+    Item.create!(@existing_item_2)
+    @patcher = DataPatcher.new
   end
+
+  def patcher
+    @patcher
+  end
+
+  it "provides an addition patch including the key and the attributes" do
+    patcher.analyze_records(:asin, @existing_items)
+    patcher.analyze_record(:asin, { :asin => "123", :title => "Hello", :summary => "The best of hello world" } )
+    patcher.patch.should == {
+      :added => [{ :asin => "123", :title => "Hello", :summary => "The best of hello world" }]
+    }
+  end
+
+  it "provides a modification patch including the key and updated attributes" do
+    patcher.analyze_records(:asin, @existing_items)
+    patcher.analyze_record(:asin, { 
+      :asin => "0471777099", # key
+      :title => "Mastering Data Warehouse Aggregates (Hard cover)", # changed data
+      :summary => "The first book to provide in-depth coverage of star schema aggregates..."}) # unchanged data
+    patcher.patch.should == {
+      :modified => [{ :asin => "0471777099", :title => "Mastering Data Warehouse Aggregates (Hard cover)"}]
+    }
+  end
+
 end

spec/spec_helper.rb

@@ -1,3 +1,4 @@
+require 'rubygems'
 require 'spec'
 
 $LOAD_PATH.unshift(File.dirname(__FILE__))
@@ -7,3 +8,23 @@
 Spec::Runner.configure do |config|
 
 end
+
+require 'active_record'
+require 'active_record/connection_adapters/mysql_adapter'
+
+require 'yaml'
+
+# database configuration and fixtures setup
+
+ActiveRecord::Base.establish_connection(YAML.load(IO.read(File.dirname(__FILE__) + "/database.yml")))
+
+# Load Models
+Dir[File.dirname(__FILE__) + "/models/*.rb"].sort.each do |file|
+  require file.gsub(/\.rb$/, '')
+end
+
+# Set up database tables and records
+Dir[File.dirname(__FILE__) + "/db/migrations/*.rb"].each do |file|
+  require file.gsub(/\.rb$/, '')
+end
+