Add support for lambdas when specifying lastmod

README.rdoc

@@ -71,13 +71,14 @@ To ping search engines, call <code>ping_search_engines</code> after you generate
   sitemap.generate
   sitemap.ping_search_engines
 
-=== Change Frequency and Priority
+=== Change Frequency, Priority and Last Modified
 
-You can control "changefreq" and "priority" values for each record individually by passing lambdas instead of fixed values:
+You can control "changefreq", "priority" and "lastmod" values for each record individually by passing lambdas instead of fixed values:
 
   sitemap.add(Posts,
     :change_frequency => lambda {|post| ... },
-    :priority         => lambda {|post| ... }
+    :priority         => lambda {|post| ... },
+    :last_modified    => lambda {|post| ... }
   )
 
 === Find Methods

lib/big_sitemap.rb

@@ -112,8 +112,13 @@ def generate
             find_options.update(:limit => limit, :offset => offset) if num_batches > 1
 
             model.send(find_method, find_options).each do |record|
-              last_mod_method = pick_method(record, TIMESTAMP_METHODS)
-              last_mod = last_mod_method.nil? ? Time.now : record.send(last_mod_method)
+              last_mod = options[:last_modified]
+              if last_mod.is_a?(Proc)
+                last_mod = last_mod.call(record)
+              elsif last_mod.nil?
+                last_mod_method = pick_method(record, TIMESTAMP_METHODS)
+                last_mod = last_mod_method.nil? ? Time.now : record.send(last_mod_method)
+              end
 
               param_method = pick_method(record, PARAM_METHODS)
 

test/big_sitemap_test.rb

@@ -130,6 +130,11 @@ def teardown
       assert_equal TestModel.new.priority.to_s, elements(first_sitemaps_model_file, 'priority').first.text
     end
 
+    should 'be able to use a lambda to specify lastmod' do
+      generate_one_sitemap_model_file(:last_modified => lambda {|m| m.updated_at})
+      assert_equal TestModel.new.updated_at.utc.strftime('%Y-%m-%dT%H:%M:%S+00:00'), elements(first_sitemaps_model_file, 'lastmod').first.text
+    end
+
     should 'contain two loc element' do
       generate_two_model_sitemap_files
       assert_equal 2, num_elements(first_sitemaps_model_file, 'loc')

test/fixtures/test_model.rb

@@ -11,6 +11,10 @@ def priority
     0.8
   end
 
+  def updated_at
+    Time.at(1000000000)
+  end
+
   class << self
     def count_for_sitemap
       self.find_for_sitemap.size