Avoid to affect the parent when adding orderable config in inherited …

…class

lib/mongoid/orderable/orderable_class.rb

@@ -34,12 +34,12 @@ def add_db_index
 
       def save_configuration
         klass.orderable_configurations ||= {}
-        klass.orderable_configurations[column_name] = configuration
+        klass.orderable_configurations = klass.orderable_configurations.merge(column_name => configuration)
       end
 
       def add_callbacks
         klass.add_orderable_callbacks
       end
     end
   end
-end
+end

spec/mongoid/orderable_spec.rb

@@ -689,6 +689,17 @@ def positions
         end.to change(first_apple, :position).from(top_pos).to bottom_pos
       end
     end
+
+    describe 'add orderable configurations in inherited class' do
+      it 'does not affect the orderable configurations of parent class and sibling class' do
+        class Apple
+          orderable :column => :serial
+        end
+        expect(Fruit.orderable_configurations).not_to eq Apple.orderable_configurations
+        expect(Orange.orderable_configurations).not_to eq Apple.orderable_configurations
+        expect(Fruit.orderable_configurations).to eq Orange.orderable_configurations
+      end
+    end
   end
 
   describe ForeignKeyDiffersOrderable do