Allow to configure a readonly DB connection

src/pretix/base/exporters/orderlist.py

@@ -315,9 +315,8 @@ class OrderListExporter(MultiSheetListExporter):
             for id, vn in payment_methods:
                 headers.append(_('Paid by {method}').format(method=vn))
 
-        if self.event_object_cache:
-            # get meta_data labels from first cached event if any
-            headers += next(iter(self.event_object_cache.values())).meta_data.keys()
+        # get meta_data labels from first cached event
+        headers += next(iter(self.event_object_cache.values())).meta_data.keys()
         yield headers
 
         full_fee_sum_cache = {
@@ -504,9 +503,8 @@ class OrderListExporter(MultiSheetListExporter):
         headers.append(_('External customer ID'))
         headers.append(_('Payment providers'))
 
-        if self.event_object_cache:
-            # get meta_data labels from first cached event if any
-            headers += next(iter(self.event_object_cache.values())).meta_data.keys()
+        # get meta_data labels from first cached event
+        headers += next(iter(self.event_object_cache.values())).meta_data.keys()
         yield headers
 
         yield self.ProgressSetTotal(total=qs.count())
@@ -709,9 +707,9 @@ class OrderListExporter(MultiSheetListExporter):
             _('Position order link')
         ]
 
+        # get meta_data labels from first cached event
+        meta_data_labels = next(iter(self.event_object_cache.values())).meta_data.keys()
         if has_subevents:
-            # get meta_data labels from first cached event
-            meta_data_labels = next(iter(self.event_object_cache.values())).meta_data.keys()
             headers += meta_data_labels
         yield headers
 

src/pretix/settings.py

@@ -157,7 +157,7 @@ DATABASES = {
         'HOST': config.get('database', 'host', fallback=''),
         'PORT': config.get('database', 'port', fallback=''),
         'CONN_MAX_AGE': 0 if db_backend == 'sqlite3' else 120,
-        'CONN_HEALTH_CHECKS': db_backend != 'sqlite3',  # Will only be used from Django 4.1 onwards
+        'CONN_HEALTH_CHECKS': db_backend != 'sqlite3',
         'DISABLE_SERVER_SIDE_CURSORS': db_disable_server_side_cursors,
         'OPTIONS': db_options,
         'TEST': {}
@@ -179,6 +179,21 @@ if config.has_section('replica'):
     }
     DATABASE_ROUTERS = ['pretix.helpers.database.ReplicaRouter']
 
+if config.has_section('dbreadonly'):
+    DATABASES['readonly'] = {
+        'ENGINE': 'django.db.backends.' + db_backend,
+        'NAME': config.get('dbreadonly', 'name', fallback=DATABASES['default']['NAME']),
+        'USER': config.get('dbreadonly', 'user', fallback=DATABASES['default']['USER']),
+        'PASSWORD': config.get('dbreadonly', 'password', fallback=DATABASES['default']['PASSWORD']),
+        'HOST': config.get('dbreadonly', 'host', fallback=DATABASES['default']['HOST']),
+        'PORT': config.get('dbreadonly', 'port', fallback=DATABASES['default']['PORT']),
+        'CONN_MAX_AGE': 0,  # do not spam primary with open connections as long as readonly is only used occasionally
+        'CONN_HEALTH_CHECKS': db_backend != 'sqlite3',
+        'DISABLE_SERVER_SIDE_CURSORS': db_disable_server_side_cursors,
+        'OPTIONS': db_options,
+        'TEST': {}
+    }
+
 STATIC_URL = config.get('urls', 'static', fallback='/static/')
 
 MEDIA_URL = config.get('urls', 'media', fallback='/media/')