[PUI] Child item table (#6334)

* Add child stock item table

* Fix stock item splitting bug

- StockItem tree was not being rebuilt correctly
- Add unit tests

* Annotate StockItem serializer with "child_items" count

* Show or hide "child items" panel

* Account for case where tree_id is zero

InvenTree/stock/api.py

@@ -655,6 +655,16 @@ class StockFilter(rest_filters.FilterSet):
             return queryset.filter(installed_items__gt=0)
         return queryset.filter(installed_items=0)
 
+    has_child_items = rest_filters.BooleanFilter(
+        label='Has child items', method='filter_has_child_items'
+    )
+
+    def filter_has_child_items(self, queryset, name, value):
+        """Filter stock items by "belongs_to" field being empty."""
+        if str2bool(value):
+            return queryset.filter(child_items__gt=0)
+        return queryset.filter(child_items=0)
+
     sent_to_customer = rest_filters.BooleanFilter(
         label='Sent to customer', method='filter_sent_to_customer'
     )

InvenTree/stock/filters.py

@@ -3,6 +3,8 @@
 from django.db.models import F, Func, IntegerField, OuterRef, Q, Subquery
 from django.db.models.functions import Coalesce
 
+from sql_util.utils import SubqueryCount
+
 import stock.models
 
 
@@ -33,3 +35,23 @@ def annotate_location_items(filter: Q = None):
         0,
         output_field=IntegerField(),
     )
+
+
+def annotate_child_items():
+    """Construct a queryset annotation which returns the number of children below a certain StockItem node in a StockItem tree."""
+    child_stock_query = stock.models.StockItem.objects.filter(
+        tree_id=OuterRef('tree_id'),
+        lft__gt=OuterRef('lft'),
+        rght__lt=OuterRef('rght'),
+        level__gte=OuterRef('level'),
+    )
+
+    return Coalesce(
+        Subquery(
+            child_stock_query.annotate(
+                count=Func(F('pk'), function='COUNT', output_field=IntegerField())
+            ).values('count')
+        ),
+        0,
+        output_field=IntegerField(),
+    )

InvenTree/stock/serializers.py

@@ -170,6 +170,7 @@ class StockItemSerializer(InvenTree.serializers.InvenTreeTagModelSerializer):
             'allocated',
             'expired',
             'installed_items',
+            'child_items',
             'stale',
             'tracking_items',
             'tags',
@@ -288,6 +289,9 @@ class StockItemSerializer(InvenTree.serializers.InvenTreeTagModelSerializer):
         # Annotate with the total number of "installed items"
         queryset = queryset.annotate(installed_items=SubqueryCount('installed_parts'))
 
+        # Annotate with the total number of "child items" (split stock items)
+        queryset = queryset.annotate(child_items=stock.filters.annotate_child_items())
+
         return queryset
 
     status_text = serializers.CharField(source='get_status_display', read_only=True)
@@ -315,6 +319,7 @@ class StockItemSerializer(InvenTree.serializers.InvenTreeTagModelSerializer):
     allocated = serializers.FloatField(required=False)
     expired = serializers.BooleanField(required=False, read_only=True)
     installed_items = serializers.IntegerField(read_only=True, required=False)
+    child_items = serializers.IntegerField(read_only=True, required=False)
     stale = serializers.BooleanField(required=False, read_only=True)
     tracking_items = serializers.IntegerField(read_only=True, required=False)