Merge 231a1ca73f into 29cedc5271

CONTRIBUTORS

@@ -0,0 +1,3 @@
+Author: Stephan Peijnik <spe@anexia.at>
+ANEXIA Internetdienstleistungs GmbH
+http://www.anexia.at/

dbtemplates/loader.py

@@ -4,6 +4,7 @@ from django.template import TemplateDoesNotExist
 from dbtemplates.conf import settings
 from dbtemplates.models import Template
 from dbtemplates.utils.cache import cache, get_cache_key, set_and_return
+from dbtemplates.utils.cache import get_cache_notfound_key
 from django.template.loader import BaseLoader
 
 
@@ -19,6 +20,18 @@ class Loader(BaseLoader):
     is_usable = True
 
     def load_template_source(self, template_name, template_dirs=None):
+        # The logic should work like this:
+        # * Try to find the template in the cache. If found, return it.
+        # * Now check the cache if a lookup for the given template
+        #   has failed lately and hand over control to the next template 
+        #   loader waiting in line.
+        # * If this still did not fail we first try to find a site-specific
+        #   template in the database.
+        # * On a failure from our last attempt we try to load the global
+        #   template from the database.
+        # * If all of the above steps have failed we generate a new key
+        #   in the cache indicating that queries failed, with the current
+        #   timestamp.
         site = Site.objects.get_current()
         display_name = 'dbtemplates:%s:%s:%s' % (settings.DATABASE_ENGINE,
                                                  template_name, site.domain)
@@ -30,15 +43,32 @@ class Loader(BaseLoader):
                     return backend_template, template_name
             except:
                 pass
+
+        # Not found in cache, move on.
+        cache_notfound_key = get_cache_notfound_key(template_name)
+        if cache:
+            try:
+                notfound = cache.get(cache_notfound_key)
+                if notfound:
+                    raise TemplateDoesNotExist(template_name)
+            except:
+                raise TemplateDoesNotExist(template_name)
+        
+        # Not marked as not-found, move on...
+
         try:
-            template = Template.objects.get(name__exact=template_name)
+            template = Template.objects.get(name__exact=template_name, 
+                                            sites__in=[site.id])
             return set_and_return(cache_key, template.content, display_name)
-        except (Template.MultipleObjectsReturned, Template.DoesNotExist):
+        except Template.DoesNotExist:
             try:
                 template = Template.objects.get(
-                    name__exact=template_name, sites__in=[site.id])
+                    name__exact=template_name)
                 return set_and_return(
                     cache_key, template.content, display_name)
             except Template.DoesNotExist:
                 pass
+
+        # Mark as not-found in cache.
+        cache.set(cache_notfound_key, '1')
         raise TemplateDoesNotExist(template_name)

dbtemplates/utils/cache.py

@@ -15,6 +15,12 @@ def get_cache_key(name):
     current_site = Site.objects.get_current()
     return 'dbtemplates::%s::%s' % (name, current_site.pk)
 
+def get_cache_notfound_key(name):
+    return get_cache_key(name)+'::notfound'
+
+def remove_notfound_key(instance):
+    # Remove notfound key as soon as we save the template.
+    cache.delete(get_cache_notfound_key(instance.name))
 
 def set_and_return(cache_key, content, display_name):
     # Save in cache backend explicitly if manually deleted or invalidated
@@ -29,6 +35,7 @@ def add_template_to_cache(instance, **kwargs):
     in the database was added or changed.
     """
     remove_cached_template(instance)
+    remove_notfound_key(instance)
     cache.set(get_cache_key(instance.name), instance.content)