Added :synchronize_keys to the import options so importing can synchronize on fields beside the primary key.

https://github.com/zdennis/activerecord-import/issues/16

lib/activerecord-import/import.rb

@@ -212,7 +212,8 @@ class ActiveRecord::Base
       end
 
       if options[:synchronize]
-        synchronize( options[:synchronize] )
+        sync_keys = options[:synchronize_keys] || [self.primary_key]
+        synchronize( options[:synchronize], sync_keys)
       end
 
       return_obj.num_inserts = 0 if return_obj.num_inserts.nil?

lib/activerecord-import/synchronize.rb

@@ -8,17 +8,29 @@ module ActiveRecord # :nodoc:
     #
     # 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)
+    def self.synchronize(instances, keys=[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" )
+      conditions = {}
+      order = ""
       
-      instances.each_with_index do |instance, index|
+      key_values = keys.map { |key| instances.map(&"#{key}".to_sym) }
+      keys.zip(key_values).each { |key, values| conditions[key] = values }
+      order = keys.map{ |key| "#{key} ASC" }.join(",")
+      
+      klass = instances.first.class
+
+      fresh_instances = klass.find( :all, :conditions=>conditions, :order=>order )
+      instances.each do |instance|
+        matched_instance = fresh_instances.detect do |fresh_instance|
+          keys.all?{ |key| fresh_instance.send(key) == instance.send(key) }
+        end
+        
+        if matched_instance
           instance.clear_aggregation_cache
           instance.clear_association_cache
-        instance.instance_variable_set '@attributes', fresh_instances[index].attributes
+          instance.instance_variable_set '@attributes', matched_instance.attributes
+        end
       end
     end
 

test/import_test.rb

@@ -66,6 +66,26 @@ describe "#import" do
     end
   end
   
+  context "with :synchronize option" do
+    context "synchronizing on new records" do
+      let(:new_topics) { Build(3, :topics) }
+    
+      it "doesn't reload any data (doesn't work)" do
+        Topic.import new_topics, :synchronize => new_topics
+        assert new_topics.all?(&:new_record?), "No record should have been reloaded"
+      end
+    end
+    
+    context "synchronizing on new records with explicit conditions" do
+      let(:new_topics) { Build(3, :topics) }
+
+      it "reloads data for existing in-memory instances" do
+        Topic.import(new_topics, :synchronize => new_topics, :synchronize_key => [:title] )
+        assert new_topics.all?(&:new_record?), "Records should have been reloaded"
+      end      
+    end
+  end
+  
   context "with an array of unsaved model instances" do
     let(:topic) { Build(:topic, :title => "The RSpec Book", :author_name => "David Chelimsky")}
     let(:topics) { Build(9, :topics) }