Ensure named_scope#empty? uses count query. [#262 state:resolved]

Signed-off-by: Pratik Naik <pratiknaik@gmail.com>

activerecord/lib/active_record/named_scope.rb

@@ -102,7 +102,7 @@ class Scope
       attr_reader :proxy_scope, :proxy_options
 
       [].methods.each do |m|
-        unless m =~ /(^__|^nil\?|^send|^object_id$|class|extend|find|count|sum|average|maximum|minimum|paginate|first|last)/
+        unless m =~ /(^__|^nil\?|^send|^object_id$|class|extend|find|count|sum|average|maximum|minimum|paginate|first|last|empty?)/
           delegate m, :to => :proxy_found
         end
       end
@@ -135,6 +135,10 @@ def last(*args)
         end
       end
 
+      def empty?
+        @found ? @found.empty? : count.zero?
+      end
+
       protected
       def proxy_found
         @found || load_found

activerecord/test/cases/named_scope_test.rb

@@ -146,4 +146,12 @@ def test_first_and_last_find_options_should_use_query_when_results_are_loaded
     end
   end
 
+  def test_empty_should_not_load_results
+    topics = Topic.base
+    assert_queries(2) do
+      topics.empty?  # use count query
+      topics.collect # force load
+      topics.empty?  # use loaded (no query)
+    end
+  end
 end