CustomContent: Add descendantOf parameter to API

This patch adds a new optional parameter to the getContentByFilter API
call to be able to retrieve all descendant nodes using the MPTT model
fields.

With this new parameter it's possible to filter all the nodes below a
specific topic node, useful when combining with other filters like kind
or tags.

kolibri/core/content/api.py

@@ -272,6 +272,7 @@ class ContentNodeFilter(IdFilter):
     rght__lt = NumberFilter(field_name="rght", lookup_expr="lt")
     authors = CharFilter(method="filter_by_authors")
     tags = CharFilter(method="filter_by_tags")
+    descendant_of = UUIDFilter(method="filter_descendant_of")
 
     class Meta:
         model = models.ContentNode
@@ -299,6 +300,20 @@ def filter_by_tags(self, queryset, name, value):
         tags = value.split(",")
         return queryset.filter(tags__tag_name__in=tags).order_by("lft")
 
+    def filter_descendant_of(self, queryset, name, value):
+        """
+        Show content that is descendant of the given node
+
+        :param queryset: all content nodes for this channel
+        :param value: the root node to filter descendant of
+        :return: all descendants content
+        """
+        try:
+            node = models.ContentNode.objects.values("lft", "rght", "tree_id").get(pk=value)
+        except (models.ContentNode.DoesNotExist, ValueError):
+            return queryset.none()
+        return queryset.filter(lft__gt=node["lft"], rght__lt=node["rght"], tree_id=node["tree_id"])
+
     def filter_kind(self, queryset, name, value):
         """
         Show only content of a given kind.

kolibri/plugins/learn/assets/src/views/ChannelRenderer/CustomContentRenderer.vue

@@ -159,6 +159,7 @@
             max_results: options.maxResults ? options.maxResults : 50,
             kind: kind,
             kind_in: kinds,
+            descendant_of: options.descendantOf,
           },
         })
           .then(contentNodes => {

packages/hashi/src/kolibri.js

@@ -114,6 +114,8 @@ export default class Kolibri extends BaseShim {
        * an array of matching metadata
        * @param {Object} options - The different options to filter by
        * @param {string=} options.parent - id of the parent node to filter by, or 'self'
+       * @param {string=} options.descendantOf - id of the root node to filter
+       * by, to show all descendants, not just direct children
        * @param {string[]} options.ids - an array of ids to filter by
        * @param {number} [options.maxResults=50] - the maximum number of nodes per request
        * @param {string[]} options.kinds - an array of kinds to filer by