[bug] Child fix (#12374)

* Remove outdated helper

* Fix children prop and add regression test

src/backend/InvenTree/stock/models.py

@@ -571,12 +571,11 @@ class StockItem(
         return 'SI'
 
     def get_children(self):
-        """Return a queryset of all StockItem objects which are children of this StockItem.
+        """Return a queryset of all StockItem objects which are direct children of this StockItem.
 
-        As the StockItem model is no longer a MPTT model,
+        Simply proxies the reverse foreign-key relation for the 'parent' field.
-        this function is implemented manually
         """
-        return StockItem.objects.filter(parent=self).exclude(pk=self.pk)
+        return self.children.all()
 
     def get_test_keys(self, include_installed=True):
         """Construct a flattened list of test 'keys' for this StockItem."""
@@ -2058,11 +2057,6 @@ class StockItem(
 
         return items
 
-    @property
-    def children(self):
-        """Return a list of the child items which have been split from this stock item."""
-        return self.get_descendants(include_self=False)
-
     @property
     def child_count(self):
         """Return the number of 'child' items associated with this StockItem.

src/backend/InvenTree/stock/tests.py

@@ -351,6 +351,51 @@ class StockTest(StockTestBase):
         stock.splitStock(stock.quantity, None, self.user)
         self.assertEqual(StockItem.objects.filter(part=3).count(), n + 1)
 
+    def test_child_items(self):
+        """Test the 'children' reverse relation and 'child_count' property.
+
+        Regression test: StockItem previously defined a 'children' property
+        (shadowed by the reverse FK accessor, and referencing a method which no
+        longer exists on the model). The property has been removed - 'children'
+        must resolve to the reverse foreign-key manager for the 'parent' field.
+        """
+        part = Part.objects.create(
+            name='Child test part', description='A part for child item testing'
+        )
+
+        parent = StockItem.objects.create(part=part, quantity=100)
+
+        self.assertEqual(parent.children.count(), 0)
+        self.assertEqual(parent.child_count, 0)
+        self.assertEqual(parent.get_children().count(), 0)
+
+        # Split off two child items
+        child_1 = parent.splitStock(10, None, self.user)
+        child_2 = parent.splitStock(20, None, self.user)
+
+        parent.refresh_from_db()
+        self.assertEqual(parent.quantity, 70)
+
+        children = parent.children.all()
+
+        self.assertEqual(children.count(), 2)
+        self.assertEqual(parent.child_count, 2)
+        self.assertIn(child_1, children)
+        self.assertIn(child_2, children)
+
+        # get_children() proxies the same relation
+        self.assertEqual(
+            list(parent.get_children().order_by('pk')), list(children.order_by('pk'))
+        )
+
+        # Only *direct* children are included
+        grandchild = child_1.splitStock(5, None, self.user)
+
+        self.assertEqual(parent.child_count, 2)
+        self.assertEqual(child_1.child_count, 1)
+        self.assertIn(grandchild, child_1.children.all())
+        self.assertNotIn(grandchild, parent.children.all())
+
     def test_stocktake(self):
         """Test stocktake function."""
         # Perform stocktake