Implement created_at and updated_at as properties fro CRUDEvents

Remove created_at field from core models.

Advances #182.

aleksis/core/mixins.py

+from datetime import datetime
 from typing import Any, Callable, Optional
 
 from django.contrib.contenttypes.models import ContentType
@@ -8,9 +9,34 @@ from easyaudit.models import CRUDEvent
 from jsonstore.fields import JSONField, JSONFieldMixin
 
 
-class ExtensibleModel(models.Model):
-    """ Allow injection of fields and code from AlekSIS apps to extend
-    model functionality.
+class CRUDMixin(models.Model):
+    class Meta:
+        abstract = True
+
+    @property
+    def crud_events(self) -> QuerySet:
+        """Get all CRUD events connected to this object from easyaudit."""
+
+        content_type = ContentType.objects.get_for_model(self)
+
+        return CRUDEvent.objects.filter(
+            object_id=self.pk, content_type=content_type
+        ).select_related("user")
+
+
+class ExtensibleModel(CRUDMixin):
+    """ Base model for all objects in AlekSIS apps
+
+    This base model ensures all objects in AlekSIS apps fulfill the
+    following properties:
+
+     * crud_events property to retrieve easyaudit's CRUD event log
+     * created_at and updated_at properties based n CRUD events
+     * Allow injection of fields and code from AlekSIS apps to extend
+       model functionality.
+
+    Injection of fields and code
+    ============================
 
     After all apps have been loaded, the code in the `model_extensions` module
     in every app is executed. All code that shall be injected into a model goes there.
@@ -43,8 +69,24 @@ class ExtensibleModel(models.Model):
         - Dominik George <dominik.george@teckids.org>
     """
 
+    @property
+    def created_at(self) -> Optional[datetime]:
+        """ Determine creation timestamp from CRUD log """
+
+        event = self.crud_events.filter(event_type=CRUDEvent.CREATE).latest("datetime")
+        if event:
+            return event.datetime
+
+    @property
+    def updated_at(self) -> Optional[datetime]:
+        """ Determine last timestamp from CRUD log """
+
+        event = self.crud_events.latest("datetime")
+        if event:
+            return event.datetime
+
     extended_data = JSONField(default=dict, editable=False)
-    
+
     @classmethod
     def _safe_add(cls, obj: Any, name: Optional[str]) -> None:
         # Decide the name for the attribute
@@ -100,18 +142,3 @@ class ExtensibleModel(models.Model):
 
     class Meta:
         abstract = True
-
-
-class CRUDMixin(models.Model):
-    class Meta:
-        abstract = True
-
-    @property
-    def crud_events(self) -> QuerySet:
-        """Get all CRUD events connected to this object from easyaudit."""
-
-        content_type = ContentType.objects.get_for_model(self)
-
-        return CRUDEvent.objects.filter(
-            object_id=self.pk, content_type=content_type
-        ).select_related("user")

aleksis/core/models.py

@@ -236,7 +236,7 @@ class Group(ExtensibleModel):
         return "%s (%s)" % (self.name, self.short_name)
 
 
-class Activity(models.Model):
+class Activity(ExtensibleModel):
     user = models.ForeignKey("Person", on_delete=models.CASCADE, related_name="activities")
 
     title = models.CharField(max_length=150, verbose_name=_("Title"))
@@ -244,8 +244,6 @@ class Activity(models.Model):
 
     app = models.CharField(max_length=100, verbose_name=_("Application"))
 
-    created_at = models.DateTimeField(auto_now_add=True, verbose_name=_("Created at"))
-
     def __str__(self):
         return self.title
 
@@ -254,7 +252,7 @@ class Activity(models.Model):
         verbose_name_plural = _("Activities")
 
 
-class Notification(models.Model):
+class Notification(ExtensibleModel):
     sender = models.CharField(max_length=100, verbose_name=_("Sender"))
     recipient = models.ForeignKey("Person", on_delete=models.CASCADE, related_name="notifications")
 
@@ -265,8 +263,6 @@ class Notification(models.Model):
     read = models.BooleanField(default=False, verbose_name=_("Read"))
     sent = models.BooleanField(default=False, verbose_name=_("Sent"))
 
-    created_at = models.DateTimeField(auto_now_add=True, verbose_name=_("Created at"))
-
     def __str__(self):
         return self.title
 
@@ -280,7 +276,7 @@ class Notification(models.Model):
         verbose_name_plural = _("Notifications")
 
 
-class Announcement(models.Model):
+class Announcement(ExtensibleModel):
     title = models.CharField(max_length=150, verbose_name=_("Title"))
     description = models.TextField(max_length=500, verbose_name=_("Description"), blank=True)
     link = models.URLField(blank=True, verbose_name=_("Link"))