Refuse to update on old MySQL

src/pretix/base/migrations/0102_auto_20181017_0024.py

@@ -1,7 +1,10 @@
 # Generated by Django 2.1 on 2018-10-17 00:24
 
 import jsonfallback.fields
+from django.core.exceptions import ImproperlyConfigured
 from django.db import migrations
+from django_mysql.checks import mysql_connections
+from django_mysql.utils import connection_is_mariadb
 
 
 def set_attendee_name_parts(apps, schema_editor):
@@ -22,12 +25,40 @@ def set_attendee_name_parts(apps, schema_editor):
         ia.save(update_fields=['name_parts'])
 
 
+def check_mysqlversion(apps, schema_editor):
+    errors = []
+    any_conn_works = False
+    conns = list(mysql_connections())
+    found = 'Unknown version'
+    for alias, conn in conns:
+        if connection_is_mariadb(conn) and hasattr(conn, 'mysql_version'):
+            if conn.mysql_version >= (10, 2, 7):
+                any_conn_works = True
+            else:
+                found = 'MariaDB ' + '.'.join(str(v) for v in conn.mysql_version)
+        elif hasattr(conn, 'mysql_version'):
+            if conn.mysql_version >= (5, 7):
+                any_conn_works = True
+            else:
+                found = 'MySQL ' + '.'.join(str(v) for v in conn.mysql_version)
+
+    if conns and not any_conn_works:
+        raise ImproperlyConfigured(
+            'As of pretix 2.2, you need MySQL 5.7+ or MariaDB 10.2.7+ to run pretix. However, we detected a '
+            'database connection to {}'.format(found)
+        )
+    return errors
+
+
 class Migration(migrations.Migration):
     dependencies = [
         ('pretixbase', '0101_auto_20181025_2255'),
     ]
 
     operations = [
+        migrations.RunPython(
+            check_mysqlversion, migrations.RunPython.noop
+        ),
         migrations.RenameField(
             model_name='cartposition',
             old_name='attendee_name',