Pulled in ActiveRecord synchronize functionality from the old ar-extensions code base.

https://github.com/zdennis/activerecord-import/issues#issue/6

lib/activerecord-import/base.rb

@@ -25,3 +25,4 @@ end
 this_dir = Pathname.new File.dirname(__FILE__)
 require this_dir.join("import")
 require this_dir.join("active_record/adapters/abstract_adapter")
+require this_dir.join("synchronize")

lib/activerecord-import/synchronize.rb

@@ -0,0 +1,30 @@
+module ActiveRecord # :nodoc:
+  class Base # :nodoc:
+      
+    # Synchronizes the passed in ActiveRecord instances with data
+    # from the database. This is like calling reload
+    # on an individual ActiveRecord instance but it is intended for use on
+    # multiple instances. 
+    #
+    # This uses one query for all instance updates and then updates existing
+    # instances rather sending one query for each instance
+    def self.synchronize(instances, key=self.primary_key)
+      return if instances.empty?
+      
+      keys = instances.map(&"#{key}".to_sym)
+      klass = instances.first.class
+      fresh_instances = klass.find( :all, :conditions=>{ key=>keys }, :order=>"#{key} ASC" )
+
+      instances.each_with_index do |instance, index|
+        instance.clear_aggregation_cache
+        instance.clear_association_cache
+        instance.instance_variable_set '@attributes', fresh_instances[index].attributes
+      end
+    end
+
+    # See ActiveRecord::ConnectionAdapters::AbstractAdapter.synchronize
+    def synchronize(instances, key=ActiveRecord::Base.primary_key)
+      self.class.synchronize(instances, key)
+    end
+  end
+end