Add _none-option to ModelChoiceField and filters for organizer and event-permission in event-typeahead (#6224)

* Add optional filters for organizer and event-permission on event-typeahead

* include _none option only if no search query given

Co-authored-by: luelista <weller@rami.io>

* allow _none in Select2, add ModelChoiceFieldWithNone

* fix flake8

---------

Co-authored-by: luelista <weller@rami.io>

src/pretix/control/forms/__init__.py

@@ -461,3 +461,31 @@ class SalesChannelCheckboxSelectMultiple(forms.CheckboxSelectMultiple):
             **super().create_option(name, value, label, selected, index, subindex, attrs),
             "plugin_missing": plugin and plugin not in self.event.get_plugins(),
         }
+
+
+class ModelChoiceIteratorWithNone(forms.models.ModelChoiceIterator):
+    # see django.forms.models.ModelChoiceIterator for original implementation
+    def __iter__(self):
+        if self.field.empty_label is not None:
+            yield ("", self.field.empty_label)
+        if self.field.none_label is not None:
+            yield ("_none", self.field.none_label)
+        queryset = self.queryset
+        # Can't use iterator() when queryset uses prefetch_related()
+        if not queryset._prefetch_related_lookups:
+            queryset = queryset.iterator()
+        for obj in queryset:
+            yield self.choice(obj)
+
+
+class ModelChoiceFieldWithNone(forms.ModelChoiceField):
+    iterator = ModelChoiceIteratorWithNone
+
+    def __init__(self, *args, **kwargs):
+        self.none_label = kwargs.pop("none_label", None)
+        super().__init__(*args, **kwargs)
+
+    def to_python(self, value):
+        if value == "_none":
+            return value
+        return super().to_python(value)

src/pretix/control/forms/widgets.py

@@ -29,17 +29,30 @@ class Select2Mixin:
         super().__init__(*args, **kwargs)
 
     def options(self, name, value, attrs=None):
-        if value and value[0]:
-            for i, selected in enumerate(self.choices.queryset.filter(pk__in=value)):
-                yield self.create_option(
-                    None,
-                    self.choices.field.prepare_value(selected),
-                    self.choices.field.label_from_instance(selected),
-                    True,
-                    i,
-                    subindex=None,
-                    attrs=attrs
-                )
+        if not value or not value[0]:
+            return
+        has_none = "_none" in value
+        if has_none:
+            value = [v for v in value if v != "_none"]
+            yield self.create_option(
+                None,
+                "_none",
+                self.choices.field.none_label,
+                True,
+                0,
+                subindex=None,
+                attrs=attrs
+            )
+        for i, selected in enumerate(self.choices.queryset.filter(pk__in=value)):
+            yield self.create_option(
+                None,
+                self.choices.field.prepare_value(selected),
+                self.choices.field.label_from_instance(selected),
+                True,
+                i + (1 if has_none else 0),
+                subindex=None,
+                attrs=attrs
+            )
         return
 
     def optgroups(self, name, value, attrs=None):