Invoicing: Allow plugins to add data (#5452)

* Allow plugins to add data to invoices

* Add documentation

src/pretix/base/migrations/0290_invoice_plugin_data.py

@@ -0,0 +1,18 @@
+# Generated by Django 4.2.17 on 2025-09-09 09:55
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("pretixbase", "0289_invoiceline_period"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="invoice",
+            name="plugin_data",
+            field=models.JSONField(default=dict),
+        ),
+    ]

src/pretix/base/models/invoices.py

@@ -202,6 +202,7 @@ class Invoice(models.Model):
     transmission_info = models.JSONField(null=True, blank=True)
 
     file = models.FileField(null=True, blank=True, upload_to=invoice_filename, max_length=255)
+    plugin_data = models.JSONField(default=dict)
 
     objects = ScopedManager(organizer='event__organizer')
 

src/pretix/base/services/invoices.py

@@ -61,7 +61,9 @@ from pretix.base.models.tax import EU_CURRENCIES
 from pretix.base.services.tasks import (
     TransactionAwareProfiledEventTask, TransactionAwareTask,
 )
-from pretix.base.signals import invoice_line_text, periodic_task
+from pretix.base.signals import (
+    build_invoice_data, invoice_line_text, periodic_task,
+)
 from pretix.celery_app import app
 from pretix.helpers.database import OF_SELF, rolledback_transaction
 from pretix.helpers.models import modelcopy
@@ -362,6 +364,7 @@ def build_invoice(invoice: Invoice) -> Invoice:
         invoice.reverse_charge = reverse_charge
         invoice.save()
 
+        build_invoice_data.send(sender=invoice.event, invoice=invoice)
         return invoice
 
 

src/pretix/base/signals.py

@@ -596,6 +596,18 @@ multiple events. Receivers should return a subclass of pretix.base.exporter.Base
 The ``sender`` keyword argument will contain an organizer.
 """
 
+build_invoice_data = EventPluginSignal()
+"""
+Arguments: ``invoice``
+
+This signal is sent out every time an invoice is built, after the invoice model was created
+and filled and before the PDF generation task is started. You can use this to make changes
+to the invoice, but we recommend to mostly use it to add content to ``Invoice.plugin_data``.
+You are responsible for saving any changes to the database.
+
+As with all event-plugin signals, the ``sender`` keyword argument will contain the event.
+"""
+
 validate_order = EventPluginSignal()
 """
 Arguments: ``payments``, ``positions``, ``email``, ``locale``, ``invoice_address``,