Fix for nested_attributes with has_many association fails when a single record is being updated.

[#5705 state:resolved]

Signed-off-by: José Valim <jose.valim@gmail.com>

activerecord/lib/active_record/nested_attributes.rb

@@ -377,7 +377,12 @@ module ActiveRecord
       end
 
       if attributes_collection.is_a? Hash
-        attributes_collection = attributes_collection.sort_by { |index, _| index.to_i }.map { |_, attributes| attributes }
+        keys = attributes_collection.keys
+        attributes_collection = if keys.include?('id') || keys.include?(:id)
+          Array.wrap(attributes_collection)
+        else
+          attributes_collection.sort_by { |i, _| i.to_i }.map { |_, attributes| attributes }
+        end
       end
 
       association = send(association_name)

activerecord/test/cases/nested_attributes_test.rb

@@ -123,6 +123,14 @@ class TestNestedAttributesInGeneral < ActiveRecord::TestCase
     assert_equal 's1', ship.reload.name
   end
 
+ def test_has_many_association_updating_a_single_record
+    Man.accepts_nested_attributes_for(:interests)
+    man = Man.create(:name => 'John')
+    interest = man.interests.create(:topic => 'photography')
+    man.update_attributes({:interests_attributes => {:topic => 'gardening', :id => interest.id}})
+    assert_equal 'gardening', interest.reload.topic
+  end
+
 end
 
 class TestNestedAttributesOnAHasOneAssociation < ActiveRecord::TestCase