Simplify waiting for db

InvenTree/InvenTree/management/commands/wait_for_db.py

@@ -7,7 +7,7 @@ from django.core.management.base import BaseCommand
 from django.db import connections
 from django.db.utils import OperationalError
 
-import psycopg2
+from part.models import Part
 
 import time
 
@@ -26,8 +26,12 @@ class Command(BaseCommand):
             try:
                 # get the database with keyword 'default' from settings.py
                 db_conn = connections['default']
+
+                # Try to read some data from the database
+                Part.objects.count()
+
                 # prints success messge in green
                 self.stdout.write(self.style.SUCCESS('InvenTree database connected'))
-            except (OperationalError, psycopg2.OperationalError):
+            except:
                 self.stdout.write(self.style.ERROR("Database unavailable, waiting 5 seconds ..."))
                 time.sleep(5)