Add option to limit events to specific sales channels (#1867)

src/pretix/base/migrations/0172_event_sales_channels.py

@@ -0,0 +1,20 @@
+# Generated by Django 3.0.9 on 2020-12-02 12:37
+
+from django.db import migrations
+
+import pretix.base.models.fields
+from pretix.base.channels import get_all_sales_channels
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ('pretixbase', '0171_auto_20201126_1635'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='event',
+            name='sales_channels',
+            field=pretix.base.models.fields.MultiStringField(default=list(get_all_sales_channels().keys())),
+        ),
+    ]