Fix #515 -- Add check-in lists (#693)

* Data model and migration

* Some backwards compatibility

* CRUD for checkin lists

* Show and perform checkins

* Correct numbers in table and dashboard widget

* event creation and cloning

* Allow to link specific exports and pass options per query

* Play with the CSV export

* PDF export

* Collapse exports by default

* Improve PDF exporter

* Addon stuff

* Subevent stuff, pretixdroid tests

* pretixdroid tests

* Add CRUD API

* Test compatibility

* Fix test

* DB-independent sorting behavior

* Add CRUD and coyp tests

* Re-enable pretixdroid plugin

* pretixdroid config

* Tests & fixes

src/pretix/helpers/database.py

@@ -1,6 +1,7 @@
 import contextlib
 
 from django.db import transaction
+from django.db.models.expressions import OrderBy
 
 
 class DummyRollbackException(Exception):
@@ -34,3 +35,25 @@ def casual_reads():
     Kept for backwards compatibility.
     """
     yield
+
+
+class FixedOrderBy(OrderBy):
+    # Workaround for https://code.djangoproject.com/ticket/28848
+    template = '%(expression)s %(ordering)s'
+
+    def as_sql(self, compiler, connection, template=None, **extra_context):
+        if not template:
+            if self.nulls_last:
+                template = '%s NULLS LAST' % self.template
+            elif self.nulls_first:
+                template = '%s NULLS FIRST' % self.template
+        connection.ops.check_expression_support(self)
+        expression_sql, params = compiler.compile(self.expression)
+        placeholders = {
+            'expression': expression_sql,
+            'ordering': 'DESC' if self.descending else 'ASC',
+        }
+        placeholders.update(extra_context)
+        template = template or self.template
+        params = params * template.count('%(expression)s')
+        return (template % placeholders).rstrip(), params