Implement event-based caching

src/tixlbase/cache.py

@@ -0,0 +1,73 @@
+import time
+import hashlib
+
+from django.core.cache import caches
+
+
+class EventRelatedCache:
+    """
+    This object behaves exactly like the cache implementations by Django
+    but with one important difference: It stores all keys related to a
+    certain event, so you pass an event when creating this object and if
+    you store data in this cache, it is only stored for this event. The
+    main purpose of this is to be able to flush all cached data related
+    to this event at once.
+    """
+
+    def __init__(self, event, cache='default'):
+        self.cache = caches[cache]
+        self.prefix = self._build_prefix()
+        self.prefixkey = 'event:%d' % self.event.pk
+
+    def _prefix_key(self, original_key):
+        # Race conditions can happen here, but should be very very rare.
+        # We could only handle this by going _really_ lowlevel using
+        # memcached's `add` keyword instead of `set`.
+        # See also:
+        # https://code.google.com/p/memcached/wiki/NewProgrammingTricks#Namespacing
+        prefix = self.cache.get(self.prefixkey)
+        if prefix is None:
+            prefix = int(time.time())
+            self.cache.set(self.prefixkey, prefix)
+        key = 'event:%d:%d:%s' % (self.event.pk, prefix, original_key)
+        if len(key) > 200:  # Hash long keys, as memcached has a length limit
+            # TODO: Use a more efficient, non-cryptographic hash algorithm
+            key = hashlib.sha256(key.encode("UTF-8")).hexdigest()
+        return key
+
+    def clear(self):
+        try:
+            prefix = self.cache.incr(self.prefixkey, 1)
+        except ValueError:
+            prefix = int(time.time())
+            self.cache.set(self.prefixkey, prefix)
+
+    def set(self, key, value, timeout=300):
+        return self.cache.set(self._prefix_key(key), value, timeout)
+
+    def get(self, key):
+        return self.cache.get(self._prefix_key(key))
+
+    def get_many(self, keys):
+        return self.cache.get_many([self._prefix_key(key) for key in keys])
+
+    def set_many(self, values, timeout=300):
+        newvalues = {}
+        for i in values.items():
+            newvalues[self._prefix_key(i[0])] = i[1]
+        return self.cache.set_many([newvalues], timeout)
+
+    def delete(self, key):
+        return self.cache.delete(self._prefix_key(key))
+
+    def delete_many(self, keys):
+        return self.cache.delete_many([self._prefix_key(key) for key in keys])
+
+    def incr(self, key, by=1):
+        return self.cache.incr(self._prefix_key(key), by)
+
+    def decr(self, key, by=1):
+        return self.cache.decr(self._prefix_key(key), by)
+
+    def close(self):
+        pass

src/tixlbase/models.py

@@ -284,6 +284,10 @@ class Event(models.Model):
     def __str__(self):
         return self.name
 
+    def save(self, *args, **kwargs):
+        self.get_cache().clear()
+        return super().save(self, *args, **kwargs)
+
     def get_date_from_display(self):
         return _date(
             self.date_from,
@@ -298,6 +302,10 @@ class Event(models.Model):
             "DATETIME_FORMAT" if self.show_times else "DATE_FORMAT"
         )
 
+    def get_cache(self):
+        from tixlbase.cache import EventRelatedCache
+        return EventRelatedCache(self)
+
 
 class EventPermission(models.Model):
     """
@@ -353,6 +361,11 @@ class ItemCategory(models.Model):
     def __str__(self):
         return self.name
 
+    def save(self, *args, **kwargs):
+        if self.event:
+            self.event.get_cache().clear()
+        return super().save(self, *args, **kwargs)
+
 
 class Property(models.Model):
     """
@@ -377,6 +390,11 @@ class Property(models.Model):
     def __str__(self):
         return self.name
 
+    def save(self, *args, **kwargs):
+        if self.event:
+            self.event.get_cache().clear()
+        return super().save(self, *args, **kwargs)
+
 
 class PropertyValue(models.Model):
     """
@@ -405,6 +423,11 @@ class PropertyValue(models.Model):
     def __str__(self):
         return "%s: %s" % (self.prop.name, self.value)
 
+    def save(self, *args, **kwargs):
+        if self.prop:
+            self.prop.event.get_cache().clear()
+        return super().save(self, *args, **kwargs)
+
 
 class Question(models.Model):
     """
@@ -446,6 +469,11 @@ class Question(models.Model):
     def __str__(self):
         return self.question
 
+    def save(self, *args, **kwargs):
+        if self.event:
+            self.event.get_cache().clear()
+        return super().save(self, *args, **kwargs)
+
 
 class Item(models.Model):
     """
@@ -529,6 +557,11 @@ class Item(models.Model):
     def __str__(self):
         return self.name
 
+    def save(self, *args, **kwargs):
+        if self.event:
+            self.event.get_cache().clear()
+        return super().save(self, *args, **kwargs)
+
     def delete(self):
         self.deleted = True
         self.active = False
@@ -569,9 +602,6 @@ class Item(models.Model):
 
         return result
 
-    def get_cache(self):
-        return None
-
 
 class ItemVariation(models.Model):
     """
@@ -614,6 +644,11 @@ class ItemVariation(models.Model):
         verbose_name = _("Item variation")
         verbose_name_plural = _("Item variations")
 
+    def save(self, *args, **kwargs):
+        if self.item:
+            self.item.event.get_cache().clear()
+        return super().save(self, *args, **kwargs)
+
 
 class BaseRestriction(models.Model):
     """
@@ -621,6 +656,12 @@ class BaseRestriction(models.Model):
     of Items or ItemVariations. This model is just an abstract base class to be
     extended by restriction plugins.
     """
+    event = models.ForeignKey(
+        Event,
+        on_delete=models.CASCADE,
+        related_name="restrictions_%(app_label)s_%(class)s",
+        verbose_name=_("Event"),
+    )
     items = models.ManyToManyField(
         Item,
         related_name="restrictions_%(app_label)s_%(class)s",
@@ -634,3 +675,8 @@ class BaseRestriction(models.Model):
         abstract = True
         verbose_name = _("Restriction")
         verbose_name_plural = _("Restrictions")
+
+    def save(self, *args, **kwargs):
+        if self.event:
+            self.event.get_cache().clear()
+        return super().save(self, *args, **kwargs)