Refactored order_field_name out of Sortable class, instead deriving from Meta.ordering, since you have to set Meta.ordering to the order field to get the proper Sorting anyway.

adminsortable/__init__.py

@@ -1,4 +1,4 @@
-VERSION = (2, 0, 0)  # following PEP 386
+VERSION = (2, 0, 1)  # following PEP 386
 DEV_N = None
 
 

adminsortable/admin.py

@@ -246,21 +246,23 @@ class SortableAdmin(SortableAdminBase, ModelAdmin):
                 objects_dict = dict([(str(obj.pk), obj) for obj in
                     klass.objects.filter(pk__in=indexes)])
 
-                if '-{}'.format(klass.order_field_name) in klass._meta.ordering:
+                order_field_name = klass._meta.ordering[0]
+
+                if '-' in order_field_name:
                     step = -1
                     start_object = max(objects_dict.values(),
-                        key=lambda x: getattr(x, klass.order_field_name))
+                        key=lambda x: getattr(x, order_field_name))
                 else:
                     step = 1
                     start_object = min(objects_dict.values(),
-                        key=lambda x: getattr(x, klass.order_field_name))
+                        key=lambda x: getattr(x, order_field_name))
 
-                start_index = getattr(start_object, klass.order_field_name,
+                start_index = getattr(start_object, order_field_name,
                     len(indexes))
 
                 for index in indexes:
                     obj = objects_dict.get(index)
-                    setattr(obj, klass.order_field_name, start_index)
+                    setattr(obj, order_field_name, start_index)
                     obj.save()
                     start_index += step
                 response = {'objects_sorted': True}

adminsortable/models.py

@@ -23,12 +23,9 @@ class SortableMixin(models.Model):
     inherits Sortable
 
     `save` the override of save increments the last/highest value of
-    `order_field_name` by 1
+    `Meta.ordering` by 1
     """
 
-    # order = models.PositiveIntegerField(editable=False, default=1,
-    #     db_index=True)
-    order_field_name = 'order'
     is_sortable = False
     sorting_filters = ()
 
@@ -46,16 +43,25 @@ class SortableMixin(models.Model):
     def __init__(self, *args, **kwargs):
         super(SortableMixin, self).__init__(*args, **kwargs)
 
-        # get the model field defined by `order_field_name`
+        # Check that Meta.ordering contains one value
+        try:
+            self.order_field_name = self._meta.ordering[0].replace('-', '')
+        except IndexError:
+            raise ValueError(u'You must define the Meta.ordering '
+                u'property on your model.')
+
+        # get the model field defined by `Meta.ordering`
         self.order_field = self._meta.get_field(self.order_field_name)
 
         integer_fields = (models.PositiveIntegerField, models.IntegerField,
             models.PositiveSmallIntegerField, models.SmallIntegerField,
             models.BigIntegerField,)
+
+        # check that the order field is an integer type
         if not self.order_field or not isinstance(self.order_field,
                 integer_fields):
             raise NotImplemented(u'You must define the field '
-                '`order_field_name` refers to, and it must be of type: '
+                '`Meta.ordering` refers to, and it must be of type: '
                 'PositiveIntegerField, IntegerField, '
                 'PositiveSmallIntegerField, SmallIntegerField, '
                 'BigIntegerField')

sample_project/app/models.py

@@ -24,7 +24,7 @@ class Category(SimpleModel, SortableMixin):
         verbose_name_plural = 'Categories'
         ordering = ['order']
 
-    order = models.PositiveIntegerField(default=0, editable=False)
+    order = models.PositiveIntegerField(default=0)
 
 
 # A model with an override of its queryset for admin
@@ -211,8 +211,6 @@ class CustomWidget(SortableMixin, SimpleModel):
     custom_order_field = models.PositiveIntegerField(default=0, db_index=True,
         editable=False)
 
-    order_field_name = 'custom_order_field'
-
     class Meta:
         ordering = ['custom_order_field']
         verbose_name = 'Custom Widget'
@@ -231,8 +229,6 @@ class CustomWidgetComponent(SortableMixin, SimpleModel):
     widget_order = models.PositiveIntegerField(default=0, db_index=True,
         editable=False)
 
-    order_field_name = 'widget_order'
-
     class Meta:
         ordering = ['widget_order']
         verbose_name = 'Custom Widget Component'