Fix: Treegrid is loading an eternity for huge amounts of data (#3451)

* Added default max depth and lazy loading to StorageLocation

* Added default max depth and lazy loading to PartCategory

* Update API version

* lint: fix

* Added INVENTREE_TREE_DEPTH setting

* Refactored int conversion into own helper function

* Added tests

InvenTree/stock/api.py

@@ -26,7 +26,7 @@ from InvenTree.api import (APIDownloadMixin, AttachmentMixin,
                            ListCreateDestroyAPIView)
 from InvenTree.filters import InvenTreeOrderingFilter
 from InvenTree.helpers import (DownloadFile, extract_serial_numbers, isNull,
-                               str2bool)
+                               str2bool, str2int)
 from InvenTree.mixins import (CreateAPI, ListAPI, ListCreateAPI, RetrieveAPI,
                               RetrieveUpdateAPI, RetrieveUpdateDestroyAPI)
 from order.models import PurchaseOrder, SalesOrder, SalesOrderAllocation
@@ -241,6 +241,8 @@ class StockLocationList(ListCreateAPI):
 
         cascade = str2bool(params.get('cascade', False))
 
+        depth = str2int(params.get('depth', None))
+
         # Do not filter by location
         if loc_id is None:
             pass
@@ -251,6 +253,9 @@ class StockLocationList(ListCreateAPI):
             if not cascade:
                 queryset = queryset.filter(parent=None)
 
+            if cascade and depth is not None:
+                queryset = queryset.filter(level__lte=depth)
+
         else:
 
             try:
@@ -259,6 +264,9 @@ class StockLocationList(ListCreateAPI):
                 # All sub-locations to be returned too?
                 if cascade:
                     parents = location.get_descendants(include_self=True)
+                    if depth is not None:
+                        parents = parents.filter(level__lte=location.level + depth)
+
                     parent_ids = [p.id for p in parents]
                     queryset = queryset.filter(parent__in=parent_ids)