Mail: Remove redundant SQL queries

On my local test event, this saved 75 queries on sending an email due to
an N+1 query problem in the metadata querying.

src/pretix/base/invoicing/pdf.py

@@ -148,10 +148,6 @@ class NumberedCanvas(Canvas):
         self.restoreState()
 
 
-class InvoiceNotReadyException(Exception):
-    pass
-
-
 class BaseInvoiceRenderer:
     """
     This is the base class for all invoice renderers.

src/pretix/base/services/invoices.py

@@ -51,7 +51,6 @@ from django_scopes import scope, scopes_disabled
 from i18nfield.strings import LazyI18nString
 
 from pretix.base.i18n import language
-from pretix.base.invoicing.pdf import InvoiceNotReadyException
 from pretix.base.invoicing.transmission import (
     get_transmission_types, transmission_providers,
 )
@@ -505,7 +504,7 @@ def generate_invoice(order: Order, trigger_pdf=True):
     return invoice
 
 
-@app.task(base=TransactionAwareTask, throws=(InvoiceNotReadyException,))
+@app.task(base=TransactionAwareTask)
 def invoice_pdf_task(invoice: int):
     with scopes_disabled():
         i = Invoice.objects.get(pk=invoice)

src/pretix/base/services/mail.py

@@ -409,6 +409,18 @@ def mail_send_task(self, **kwargs) -> bool:
         outgoing_mail.inflight_since = now()
         outgoing_mail.save(update_fields=["status", "inflight_since"])
 
+    # Performance optimization, saves database queries later on if we resolve the known relationships
+    if outgoing_mail.event_id:
+        assert outgoing_mail.event.organizer_id == outgoing_mail.organizer.pk
+        outgoing_mail.event.organizer = outgoing_mail.organizer
+    if outgoing_mail.order_id:
+        assert outgoing_mail.order.event_id == outgoing_mail.event_id
+        outgoing_mail.order.event = outgoing_mail.event
+        outgoing_mail.order.organizer = outgoing_mail.organizer
+    if outgoing_mail.orderposition_id:
+        assert outgoing_mail.orderposition.order_id == outgoing_mail.order_id
+        outgoing_mail.orderposition.order = outgoing_mail.order
+
     headers = dict(outgoing_mail.headers)
     headers.setdefault('X-PX-Correlation', str(outgoing_mail.guid))
     email = CustomEmail(

src/pretix/base/services/placeholders.py

@@ -24,6 +24,7 @@ import logging
 from datetime import timedelta
 from decimal import Decimal
 
+from django.db.models import Prefetch, prefetch_related_objects
 from django.dispatch import receiver
 from django.utils.formats import date_format
 from django.utils.html import escape, mark_safe
@@ -35,6 +36,7 @@ from pretix.base.forms.widgets import format_placeholders_help_text
 from pretix.base.i18n import (
     LazyCurrencyNumber, LazyDate, LazyExpiresDate, LazyNumber,
 )
+from pretix.base.models import EventMetaValue
 from pretix.base.reldate import RelativeDateWrapper
 from pretix.base.settings import PERSON_NAME_SCHEMES, get_name_parts_localized
 from pretix.base.signals import (
@@ -752,6 +754,11 @@ def base_placeholders(sender, **kwargs):
             name_scheme['sample'][f]
         ))
 
+    prefetch_related_objects(
+        [sender],
+        Prefetch('meta_values', queryset=EventMetaValue.objects.select_related("property"), to_attr="meta_values_cached")
+    )
+    prefetch_related_objects([sender.organizer], Prefetch('meta_properties'))
     for k, v in sender.meta_data.items():
         ph.append(MarkdownTextPlaceholder(
             'meta_%s' % k, ['event'], lambda event, k=k: event.meta_data[k],

src/pretix/presale/templates/pretixpresale/event/resend_link.html

@@ -1,14 +1,14 @@
 {% extends "pretixpresale/event/base.html" %}
 {% load i18n %}
 {% load bootstrap3 %}
-{% block title %}{% trans "Resend order link" %}{% endblock %}
+{% block title %}{% trans "Resend order links" %}{% endblock %}
 {% block custom_header %}
     {{ block.super }}
     <meta name="robots" content="noindex, nofollow">
 {% endblock %}
 {% block content %}
     <h2>
-        {% trans "Resend order link" %}
+        {% trans "Resend order links" %}
     </h2>
     <p>
         {% blocktrans trimmed %}

src/pretix/presale/views/order.py

@@ -1510,10 +1510,7 @@ class OrderChangeMixin:
                             'max_count': iao.max_count,
                             'iao': iao,
                             'items': [i for i in items if not i.require_voucher],
-                            'items_missing': {
-                                k: v for k, v in current_addon_products_missing.items()
-                                if v and k[0].category_id == iao.addon_category_id
-                            },
+                            'items_missing': {k: v for k, v in current_addon_products_missing.items() if v},
                         })
 
         return positions