Recursive delete fix fix (#5819)

* Enable mysql checks as part of PR

* Add debug for CI

* Add delete_nodes method

- Ensure that the "parent" field is set to None before delete
- This means that we do not violate any ForeignKey constraints due to undefined order of operations

.github/workflows/qc_checks.yaml

@@ -274,7 +274,6 @@ jobs:
     runs-on: ubuntu-20.04
 
     needs: [ 'pep_style', 'pre-commit' ]
-    if: github.event_name == 'push'
 
     env:
       # Database backend configuration

InvenTree/InvenTree/models.py

@@ -660,12 +660,14 @@ class InvenTreeTree(MPTTModel):
         D) delete_children = False and delete_items = False
         """
 
+        child_nodes = self.get_descendants(include_self=False)
+
         # Case A: Delete all child items, and all child nodes.
         # - Delete all items at any lower level
         # - Delete all descendant nodes
         if delete_children and delete_items:
             self.get_items(cascade=True).delete()
-            self.get_descendants(include_self=False).delete()
+            self.delete_nodes(child_nodes)
 
         # Case B: Delete all child nodes, but move all child items up to the parent
         # - Move all items at any lower level to the parent of this item
@@ -674,7 +676,8 @@ class InvenTreeTree(MPTTModel):
             self.get_items(cascade=True).update(**{
                 self.ITEM_PARENT_KEY: self.parent
             })
-            self.get_descendants(include_self=False).delete()
+
+            self.delete_nodes(child_nodes)
 
         # Case C: Delete all child items, but keep all child nodes
         # - Remove all items directly associated with this node
@@ -692,6 +695,21 @@ class InvenTreeTree(MPTTModel):
             })
             self.get_children().update(parent=self.parent)
 
+    def delete_nodes(self, nodes):
+        """Delete  a set of nodes from the tree.
+
+        1. First, set the "parent" value for selected nodes to None
+        2. Then, perform bulk deletion of selected nodes
+
+        Step 1. is required because we cannot guarantee the order-of-operations in the db backend
+
+        Arguments:
+            nodes: A queryset of nodes to delete
+        """
+
+        nodes.update(parent=None)
+        nodes.delete()
+
     def validate_unique(self, exclude=None):
         """Validate that this tree instance satisfies our uniqueness requirements.
 

InvenTree/part/test_category.py

@@ -226,6 +226,8 @@ class CategoryTest(TestCase):
         # Clear out any existing parts
         Part.objects.all().delete()
 
+        PartCategory.objects.rebuild()
+
         # First, create a structured tree of part categories
         A = PartCategory.objects.create(
             name='A',