Fix has_many#count_records. [#865 state:resolved]

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

activerecord/lib/active_record/associations/has_many_association.rb

@@ -27,8 +27,11 @@ def count_records
           else
             @reflection.klass.count(:conditions => @counter_sql, :include => @reflection.options[:include])
           end
-
-          @target = [] and loaded if count == 0
+
+          # If there's nothing in the database and @target has no new records
+          # we are certain the current target is an empty array. This is a
+          # documented side-effect of the method that may avoid an extra SELECT.
+          @target ||= [] and loaded if count == 0
 
           if @reflection.options[:limit]
             count = [ @reflection.options[:limit], count ].min

activerecord/test/cases/associations/has_many_associations_test.rb

@@ -391,6 +391,18 @@ def test_collection_size_after_building
     assert_equal 3, company.clients_of_firm.size
   end
 
+  def test_collection_size_twice_for_regressions
+    post = posts(:thinking)
+    assert_equal 0, post.readers.size
+    # This test needs a post that has no readers, we assert it to ensure it holds,
+    # but need to reload the post because the very call to #size hides the bug.
+    post.reload
+    post.readers.build
+    size1 = post.readers.size
+    size2 = post.readers.size
+    assert_equal size1, size2
+  end
+
   def test_build_many
     company = companies(:first_firm)
     new_clients = assert_no_queries { company.clients_of_firm.build([{"name" => "Another Client"}, {"name" => "Another Client II"}]) }