First things to implement a event change log

dav_events/models/eventchange.py

@@ -0,0 +1,36 @@
+from __future__ import unicode_literals
+from django.conf import settings
+from django.db import models
+from django.utils import timezone
+from django.utils.encoding import python_2_unicode_compatible
+
+from . import get_ghost_user, get_system_user
+
+CHANGE_OPERATIONS = (
+    ('update', 'update'),
+)
+
+
+def get_system_user_id():
+    return get_system_user().id
+
+
+@python_2_unicode_compatible
+class EventChange(models.Model):
+    event = models.ForeignKey('dav_events.Event', related_name='changes')
+    timestamp = models.DateTimeField(default=timezone.now)
+    user = models.ForeignKey(settings.AUTH_USER_MODEL,
+                             default=get_system_user_id,
+                             on_delete=models.SET(get_ghost_user),
+                             related_name='+')
+
+    operation = models.CharField(max_length=20, choices=CHANGE_OPERATIONS)
+    content = models.TextField()
+
+    class Meta:
+        ordering = ['event', 'timestamp']
+
+    def __str__(self):
+        s = '{timestamp} - {user} - {operation}'
+        return s.format(operation=self.operation, timestamp=self.timestamp.strftime('%d.%m.%Y %H:%M:%S %Z'),
+                        user=self.user)