Improve "hook" for loading custom unit database

InvenTree/InvenTree/apps.py

@@ -11,6 +11,7 @@ from django.core.exceptions import AppRegistryNotReady
 from django.db import transaction
 from django.db.utils import IntegrityError
 
+import InvenTree.conversion
 import InvenTree.tasks
 from InvenTree.config import get_setting
 from InvenTree.ready import canAppAccessDatabase, isInTestMode
@@ -46,6 +47,9 @@ class InvenTreeConfig(AppConfig):
 
         self.collect_notification_methods()
 
+        # Ensure the unit registry is loaded
+        InvenTree.conversion.reload_unit_registry()
+
         if canAppAccessDatabase() or settings.TESTING_ENV:
             self.add_user_on_startup()
 

InvenTree/InvenTree/conversion.py

@@ -15,13 +15,26 @@ def get_unit_registry():
 
     # Cache the unit registry for speedier access
     if _unit_registry is None:
-        _unit_registry = pint.UnitRegistry()
-
-    # TODO: Allow for custom units to be defined in the database
+        reload_unit_registry()
 
     return _unit_registry
 
 
+def reload_unit_registry():
+    """Reload the unit registry from the database.
+
+    This function is called at startup, and whenever the database is updated.
+    """
+
+    global _unit_registry
+
+    _unit_registry = pint.UnitRegistry()
+
+    # TODO: Define some "standard" additional unitss
+
+    # TODO: Allow for custom units to be defined in the database
+
+
 def convert_physical_value(value: str, unit: str = None):
     """Validate that the provided value is a valid physical quantity.