Ticket #3453: resolve-variable.patch

django/core/serializers/python.py

@@ -89 +89 @@
             else:
                 data[field.name] = field.to_python(field_value)
                 
+        data["disable_inst_caching"] = True
         yield base.DeserializedObject(Model(**data), m2m_data)
 
 def _get_model(model_identifier):

django/core/serializers/xml_serializer.py

@@ -170 +170 @@
                     value = field.to_python(getInnerText(field_node).strip().encode(self.encoding))
                 data[field.name] = value
         
+        data["disable_inst_caching"] = True
         # Return a DeserializedObject so that the m2m data has a place to live.
         return base.DeserializedObject(Model(**data), m2m_data)
         
@@ -226 +227 @@
             inner_text.extend(getInnerText(child))
         else:
            pass
-    return "".join(inner_text)
- No newline at end of file
+    return "".join(inner_text)

django/db/models/base.py

@@ -14 +14 @@
 from django.utils.functional import curry
 from django.conf import settings
 from itertools import izip
+from weakref import WeakValueDictionary
 import types
 import sys
 import os
@@ -76 +77 @@
         # registered version.
         return get_model(new_class._meta.app_label, name, False)
 
+    def __call__(cls, *args, **kwargs):
+        if not kwargs.pop("disable_inst_caching", 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
 
@@ -94 +110 @@
     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_position = cls._meta.fields.index(cls._meta.pk)
+        if len(args) > pk_position:
+            return args[pk_position]
+        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, id):
+        return cls.__instance_cache__.get(id)
+    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)
         
@@ -194 +227 @@
         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)
 
     _prepare = classmethod(_prepare)
@@ -251 +286 @@
                 setattr(self, self._meta.pk.attname, backend.get_last_insert_id(cursor, self._meta.db_table, self._meta.pk.column))
         transaction.commit_unless_managed()
 
+        # if we're a new instance that hasn't been written in; save ourself.
+        if self._meta.has_auto_field:
+            self.__instance_cache__[getattr(self, self._meta.pk.attname)] = self
+
         # Run any post-save hooks.
         dispatcher.send(signal=signals.post_save, sender=self.__class__, instance=self)
 

django/db/models/fields/related.py

@@ -163 +163 @@
                 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
 

tests/modeltests/model_forms/models.py

@@ -244 +244 @@
 1
 >>> test_art = Article.objects.get(id=1)
 >>> test_art.headline
-'Test headline'
+u'Test headline'
 
 You can create a form over a subset of the available fields 
 by specifying a 'fields' argument to form_for_instance. 
@@ -260 +260 @@
 1
 >>> new_art = Article.objects.get(id=1)
 >>> new_art.headline
-'New headline'
+u'New headline'
 
 Add some categories and test the many-to-many form output.
 >>> new_art.categories.all()

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