Ticket #17: 5737_instance_caching.diff

django/db/models/base.py

@@ -15 +15 @@
 from django.utils.encoding import smart_str, force_unicode
 from django.conf import settings
 from itertools import izip
+from weakref import WeakValueDictionary
 import types
 import sys
 import os
@@ -76 +77 @@
         # should only be one class for each model, so we must always return the
         # registered version.
         return get_model(new_class._meta.app_label, name, False)
+    
+    def __call__(cls, *args, **kwargs):
+        if not kwargs.pop("disable_instance_cache", False) \
+            and cls._meta.has_auto_field:
+            key = cls._get_cache_key(args, kwargs)
+            if key is not None:
+                obj = cls.__instance_cache__.get(key)
+                if obj is None:
+                    obj = super(ModelBase, cls).__call__(*args, **kwargs)
+                    cls.__instance_cache__[key] = obj
+            else:
+                obj = super(ModelBase, cls).__call__(*args, **kwargs)
+        else:
+            obj = super(ModelBase, cls).__call__(*args, **kwargs)
+        return obj
 
 class Model(object):
     __metaclass__ = ModelBase
@@ -96 +112 @@
 
     def __ne__(self, other):
         return not self.__eq__(other)
+    
+    def _get_cache_key(cls, args, kwargs):
+        # this should be calculated *once*, but isn't atm
+        pk_index = cls._meta.fields.index(cls._meta.pk)
+        if len(args) > pk_index:
+            return args[pk_index]
+        pk = cls._meta.pk
+        if pk.name in kwargs:
+            return kwargs[pk.name]
+        elif pk.attname in kwargs:
+            return kwargs[pk.attname]
+        return None
+    _get_cache_key = classmethod(_get_cache_key)
+    
+    def get_cached_instance(cls, key):
+        return cls.__instance_cache__.get(key)
+    get_cached_instance = classmethod(get_cached_instance)
 
     def __init__(self, *args, **kwargs):
         dispatcher.send(signal=signals.pre_init, sender=self.__class__, args=args, kwargs=kwargs)
@@ -196 +229 @@
 
         if hasattr(cls, 'get_absolute_url'):
             cls.get_absolute_url = curry(get_absolute_url, opts, cls.get_absolute_url)
+        
+        cls.__instance_cache__ = WeakValueDictionary()
 
         dispatcher.send(signal=signals.class_prepared, sender=cls)
 
@@ -254 +289 @@
             if self._meta.has_auto_field and not pk_set:
                 setattr(self, self._meta.pk.attname, backend.get_last_insert_id(cursor, self._meta.db_table, self._meta.pk.column))
         transaction.commit_unless_managed()
+        
+        # write this instance into cache if not already present
+        if self._meta.has_auto_field:
+            self.__instance_cache__[self._get_pk_val()] = self
 
         # Run any post-save hooks.
         dispatcher.send(signal=signals.post_save, sender=self.__class__, instance=self)
@@ -315 +354 @@
         self._collect_sub_objects(seen_objs)
 
         # Actually delete the objects
+        if self._meta.has_auto_field:
+            pk = self._get_pk_val()
+            if pk is not None:
+                self.__instance_cache__.pop(pk, None)
         delete_objects(seen_objs)
 
     delete.alters_data = True

django/db/models/fields/related.py

@@ -165 +165 @@
                 if self.field.null:
                     return None
                 raise self.field.rel.to.DoesNotExist
-            other_field = self.field.rel.get_related_field()
-            if other_field.rel:
-                params = {'%s__pk' % self.field.rel.field_name: val}
-            else:
-                params = {'%s__exact' % self.field.rel.field_name: val}
-            rel_obj = self.field.rel.to._default_manager.get(**params)
+            rel_obj = self.field.rel.to.get_cached_instance(val)
+            if rel_obj is None:
+                other_field = self.field.rel.get_related_field()
+                if other_field.rel:
+                    params = {'%s__pk' % self.field.rel.field_name: val}
+                else:
+                    params = {'%s__exact' % self.field.rel.field_name: val}
+                rel_obj = self.field.rel.to._default_manager.get(**params)
             setattr(instance, cache_name, rel_obj)
             return rel_obj
 

django/db/models/query.py

@@ -1109 +1109 @@
     for cls in ordered_classes:
         seen_objs[cls] = seen_objs[cls].items()
         seen_objs[cls].sort()
+        clean_instance_cache = cls.__instance_cache__.pop
 
         # Pre notify all instances to be deleted
         for pk_val, instance in seen_objs[cls]:
             dispatcher.send(signal=signals.pre_delete, sender=cls, instance=instance)
 
         pk_list = [pk for pk,instance in seen_objs[cls]]
+        # we wipe the cache now; it's *possible* some form of a __get__ lookup
+        # may reintroduce an item after the fact with the same pk, however
+        # it is extremely unlikely
+        for x in pk_list:
+            clean_instance_cache(x, None)
+            
         for related in cls._meta.get_all_related_many_to_many_objects():
             if not isinstance(related.field, generic.GenericRelation):
                 for offset in range(0, len(pk_list), GET_ITERATOR_CHUNK_SIZE):
@@ -1148 +1155 @@
     for cls in ordered_classes:
         seen_objs[cls].reverse()
         pk_list = [pk for pk,instance in seen_objs[cls]]
+        for x in pk_list:
+            clean_instance_cache(x, None)
         for offset in range(0, len(pk_list), GET_ITERATOR_CHUNK_SIZE):
             cursor.execute("DELETE FROM %s WHERE %s IN (%s)" % \
                 (qn(cls._meta.db_table), qn(cls._meta.pk.column),

django/core/serializers/xml_serializer.py

@@ -177 +177 @@
                     value = field.to_python(getInnerText(field_node).strip())
                 data[field.name] = value
 
+        data["disable_instance_cache"] = True
         # Return a DeserializedObject so that the m2m data has a place to live.
         return base.DeserializedObject(Model(**data), m2m_data)
 

django/core/serializers/python.py

@@ -88 +88 @@
             # Handle all other fields
             else:
                 data[field.name] = field.to_python(field_value)
-
+        
+        data["disable_instance_cache"] = True
         yield base.DeserializedObject(Model(**data), m2m_data)
 
 def _get_model(model_identifier):

tests/modeltests/select_related/models.py

@@ -107 +107 @@
 1
 
 # select_related() also of course applies to entire lists, not just items.
-# Without select_related()
+# Without select_related() (note instance caching still reduces this from 9 to 5)
 >>> db.reset_queries()
 >>> world = Species.objects.all()
 >>> [o.genus.family for o in world]
 [<Family: Drosophilidae>, <Family: Hominidae>, <Family: Fabaceae>, <Family: Amanitacae>]
 >>> len(db.connection.queries)
-9
+5
 
 # With select_related():
 >>> db.reset_queries()
@@ -129 +129 @@
 >>> pea.genus.family.order.klass.phylum.kingdom.domain
 <Domain: Eukaryota>
 
-# Notice: one few query than above because of depth=1
+# Notice: instance caching saves the day; would be 7 without.
 >>> len(db.connection.queries)
-7
+1
 
 >>> db.reset_queries()
 >>> pea = Species.objects.select_related(depth=5).get(name="sativum")
 >>> pea.genus.family.order.klass.phylum.kingdom.domain
 <Domain: Eukaryota>
 >>> len(db.connection.queries)
-3
+1
 
 >>> db.reset_queries()
 >>> world = Species.objects.all().select_related(depth=2)
 >>> [o.genus.family.order for o in world]
 [<Order: Diptera>, <Order: Primates>, <Order: Fabales>, <Order: Agaricales>]
 >>> len(db.connection.queries)
-5
+1
 
 # Reset DEBUG to where we found it.
 >>> settings.DEBUG = False