more careful checking, updated test, command-line option

lib/assimilate/command.rb

@@ -31,6 +31,10 @@ def initialize
       opts.on("--domain STRING", String, "Domain value to apply to each record") do |s|
         @options[:domain] = s
       end
+
+      opts.on("--compare FIELDNAME", String, "(*extend* only) Optional field to check whether an update is current (e.g. timestamp)") do |f|
+        @options[:compare] = f
+      end
     end
   end
 

lib/assimilate/extender.rb

@@ -37,7 +37,7 @@ def is_newer(current_data, new_data)
   # if there is a field to compare on (i.e. a timestamp), then apply the update if the timestamp is newer;
   # otherwise (no timestamp) compare the hashes and apply if there are any differences.
   def apply_this_update(current_record, new_data)
-    if @comparison_field
+    if @comparison_field && current_record[@keyfield]
       is_newer(current_record[@keyfield], new_data)
     else
       current_record[@keyfield] != new_data

lib/assimilate/version.rb

@@ -1,3 +1,3 @@
 module Assimilate
-  VERSION = "0.2"
+  VERSION = "0.2.1"
 end

spec/lib/extend_spec.rb

@@ -74,7 +74,7 @@ def import_extended_data(datestamp, filename, opts = {})
     before(:all) do
       reset_catalog
       import_base_data("20120501")
-      import_extended_data("20120505", "logs1.csv")
+      import_extended_data("20120505", "logs1.csv", :compare => 'timestamp')
     end