Use Enum and constraint for valid notification types.

fedireads/models/status.py

@@ -88,6 +88,9 @@ class Tag(FedireadsModel):
         unique_together = ('user', 'book', 'name')
 
 
+NotificationType = models.TextChoices(
+    'NotificationType', 'FAVORITE REPLY TAG FOLLOW FOLLOW_REQUEST')
+
 class Notification(FedireadsModel):
     ''' you've been tagged, liked, followed, etc '''
     user = models.ForeignKey('User', on_delete=models.PROTECT)
@@ -99,18 +102,12 @@ class Notification(FedireadsModel):
     related_status = models.ForeignKey(
         'Status', on_delete=models.PROTECT, null=True)
     read = models.BooleanField(default=False)
-    notification_type = models.CharField(max_length=255)
-
-    def save(self, *args, **kwargs):
-        # TODO: there's probably a real way to do enums
-        types = [
-            'FAVORITE',
-            'REPLY',
-            'TAG',
-            'FOLLOW',
-            'FOLLOW_REQUEST'
+    notification_type = models.CharField(
+        max_length=255, choices=NotificationType.choices)
+    class Meta:
+        constraints = [
+            models.CheckConstraint(
+                check=models.Q(notification_type__in=NotificationType.values),
+                name="notification_type_valid",
+            )
         ]
-        if not self.notification_type in types:
-            raise ValueError('Invalid notitication type')
-        super().save(*args, **kwargs)
-