Update exchange rates when launching the server

- Ensures that the exchange rates don't get messed up if the base currency is changed!

InvenTree/InvenTree/apps.py

@@ -4,6 +4,7 @@ import logging
 
 from django.apps import AppConfig
 from django.core.exceptions import AppRegistryNotReady
+from django.conf import settings
 
 from InvenTree.ready import canAppAccessDatabase
 import InvenTree.tasks
@@ -19,6 +20,7 @@ class InvenTreeConfig(AppConfig):
 
         if canAppAccessDatabase():
             self.start_background_tasks()
+            self.update_exchange_rates()
 
     def start_background_tasks(self):
 
@@ -49,3 +51,49 @@ class InvenTreeConfig(AppConfig):
             'InvenTree.tasks.update_exchange_rates',
             schedule_type=Schedule.DAILY,
         )
+
+    def update_exchange_rates(self):
+        """
+        Update exchange rates each time the server is started, *if*:
+
+        a) Have not been updated recently (one day or less)
+        b) The base exchange rate has been altered
+        """
+
+        try:
+            from djmoney.contrib.exchange.models import ExchangeBackend
+            from datetime import datetime, timedelta
+            from InvenTree.tasks import update_exchange_rates
+        except AppRegistryNotReady:
+            pass
+
+        base_currency = settings.BASE_CURRENCY
+
+        update = False
+
+        try:
+            backend = ExchangeBackend.objects.get(name='InvenTreeExchange')
+
+            last_update = backend.last_update
+
+            if last_update is not None:
+                delta = datetime.now().date() - last_update.date()
+                if delta > timedelta(days=1):
+                    print(f"Last update was {last_update}")
+                    update = True
+            else:
+                # Never been updated
+                print("Exchange backend has never been updated")
+                update = True
+
+            # Backend currency has changed?
+            if not base_currency == backend.base_currency:
+                print(f"Base currency changed from {backend.base_currency} to {base_currency}")
+                update = True
+
+        except (ExchangeBackend.DoesNotExist):
+            print("Exchange backend not found - updating")
+            update = True
+
+        if update:
+            update_exchange_rates()

InvenTree/InvenTree/tasks.py

@@ -168,6 +168,7 @@ def update_exchange_rates():
 
     try:
         from InvenTree.exchange import InvenTreeExchange
+        from djmoney.contrib.exchange.models import Rate
         from django.conf import settings
     except AppRegistryNotReady:
         # Apps not yet loaded!
@@ -182,6 +183,9 @@ def update_exchange_rates():
 
     backend.update_rates(base_currency=base)
 
+    # Remove any exchange rates which are not in the provided currencies
+    Rate.objects.filter(backend="InvenTreeExchange").exclude(currency__in=settings.CURRENCIES).delete()
+
 
 def send_email(subject, body, recipients, from_email=None):
     """