Allow descending order of items

wagtailorderable/modeladmin/mixins.py

@@ -12,6 +12,10 @@
 from ..signals import pre_reorder, post_reorder
 
 
+def ordering_contains_field(ordering, field_name):
+    return bool(set(ordering) & {field_name, "-" + field_name})
+
+
 class OrderableMixinMetaClass(type):
     """
     index_order method needs to be completed with an `admin_order_field` but as sort_order_field
@@ -23,12 +27,16 @@ def __new__(cls, name, bases, attrs):
         if model and not sort_order_field:
             sort_order_field = getattr(model, 'sort_order_field', None)
         if sort_order_field:
-            # unfortunately, wagtail IndexView._get_default_ordering is currently using
-            # `model_admin.ordering` instead of `model_admin.get_ordering()`
-            # So we need to automagically set it here
+            # Ensure, that our sort field is set in "ordering", as this attribute is required by methods like
+            # wagtail's IndexView._get_default_ordering().
             if 'ordering' not in attrs:
-                attrs['ordering'] = (sort_order_field, )
-            elif sort_order_field not in attrs['ordering']:
+                opts = model._meta
+                if opts.ordering and ordering_contains_field(opts.ordering, sort_order_field):
+                    # If the model's Meta already defines an ordering with our field, we use it.
+                    attrs['ordering'] = opts.ordering
+                else:
+                    attrs['ordering'] = (sort_order_field, )
+            elif not ordering_contains_field(attrs['ordering'], sort_order_field):
                 attrs['ordering'] = (sort_order_field, ) + tuple(attrs['ordering'])
 
             # set the "sorting" column
@@ -79,17 +87,6 @@ def __init__(self, parent=None):
                 "into your model." %
                 (self.__class__.__name__, self.sort_order_field))
 
-    def get_ordering(self, request):
-        """
-        Returns a sequence defining the default ordering for results in the
-        list view.
-        """
-        if not self.ordering:
-            return (self.sort_order_field, )
-        elif self.sort_order_field not in self.ordering:
-            return (self.sort_order_field, ) + tuple(self.ordering)
-        return self.ordering
-
     def get_list_display(self, request):
         """Add `index_order` as the first column to results"""
         list_display = list(super().get_list_display(request))

wagtailorderable/static/wagtailorderable/modeladmin/js/orderablemixin.js

@@ -5,7 +5,8 @@ $(function() {
     var sorted_cols = listing_thead.find('th.sorted');
     order_header.find('a').addClass('text-replace').removeClass('icon icon-arrow-down-after icon-arrow-up-after');
     order_header.find('a').html('<span class="icon icon-order" aria-hidden="true"></span> Sort');
-    if(sorted_cols.length == 1 && order_header.hasClass('sorted') && order_header.hasClass('ascending')){
+    if(sorted_cols.length === 1 && order_header.hasClass('sorted')){
+        var isAsc = order_header.hasClass('ascending');
         order_header.find('a').attr('title', 'Restore default list ordering').attr('href', '?');
         listing_tbody.sortable({
             cursor: "move",
@@ -34,12 +35,12 @@ $(function() {
                 if ($(this).data('idx') < ui.item.index()) {
                     idx = $(movedElement).prev().data('object-pk');
                     if (idx) {
-                        params.set('after', idx);
+                        params.set(isAsc ? 'after' : 'before', idx);
                     }
                 } else if ($(this).data('idx') > ui.item.index()) {
                     idx = $(movedElement).next().data('object-pk');
                     if (idx) {
-                        params.set('before', idx);
+                        params.set(isAsc ? 'before' : 'after', idx);
                     }
                 }
 
@@ -66,6 +67,6 @@ $(function() {
         var href = new URL(window.location.href);  // we need to keep current filters
         href.searchParams.set('o', '0');
         a.attr('href', href.toString());
-        order_header.removeClass('sorted ascending');
+        order_header.removeClass('sorted ascending descending');
     }
 });