removed __getattribute__ hack from PolymorphicModel.

A somewhat cleaner solution is now used (through __init__) which
also completely removes the performance impact of __getattribute__.

.gitignore

@@ -17,6 +17,7 @@ pbackup
 mcmd.py
 dbconfig_local.py
 diffmanagement
+scrapbook.py
 
 pip-log.txt
 build

pexp/management/commands/pcmd.py

@@ -23,19 +23,18 @@ class Command(NoArgsCommand):
         print 'polycmd - sqlite test db is stored in:',settings.SQLITE_DB_PATH
         print
 
-        """
-        ModelA.objects.all().delete()
-        o=ModelA.objects.create(field1='A1')
-        o=ModelB.objects.create(field1='B1', field2='B2')
-        o=ModelC.objects.create(field1='C1', field2='C2', field3='C3')
-        print ModelA.objects.all()
-        print
-        """
-
         Project.objects.all().delete()
-        o=Project.objects.create(topic="John's gathering")
-        o=ArtProject.objects.create(topic="Sculpting with Tim", artist="T. Turner")
-        o=ResearchProject.objects.create(topic="Swallow Aerodynamics", supervisor="Dr. Winter")
+        a=Project.objects.create(topic="John's gathering")
+        b=ArtProject.objects.create(topic="Sculpting with Tim", artist="T. Turner")
+        c=ResearchProject.objects.create(topic="Swallow Aerodynamics", supervisor="Dr. Winter")
         print Project.objects.all()
         print
 
+        """
+        ModelA.objects.all().delete()
+        a=ModelA.objects.create(field1='A1')
+        b=ModelB.objects.create(field1='B1', field2='B2')
+        c=ModelC.objects.create(field1='C1', field2='C2', field3='C3')
+        print ModelA.objects.all()
+        print
+        """

pexp/models.py

@@ -20,6 +20,13 @@ class ModelB(ModelA):
 class ModelC(ModelB):
     field3 = models.CharField(max_length=10)
 
+class nModelA(models.Model):
+    field1 = models.CharField(max_length=10)
+class nModelB(nModelA):
+    field2 = models.CharField(max_length=10)
+class nModelC(nModelB):
+    field3 = models.CharField(max_length=10)
+
 
 # for Django 1.2+, test models with same names in different apps
 # (the other models with identical names are in polymorphic/tests.py)

polymorphic/base.py

@@ -73,6 +73,9 @@ class PolymorphicModelBase(ModelBase):
         # validate resulting default manager
         self.validate_model_manager(new_class._default_manager, model_name, '_default_manager')
 
+        # for __init__ function of this class (monkeypatching inheritance accessors)
+        new_class.polymorphic_super_sub_accessors_replaced = False
+
         return new_class
 
     def get_inherited_managers(self, attrs):
@@ -153,6 +156,7 @@ class PolymorphicModelBase(ModelBase):
             raise AssertionError(e)
         return manager
 
+
     # hack: a small patch to Django would be a better solution.
     # Django's management command 'dumpdata' relies on non-polymorphic
     # behaviour of the _default_manager. Therefore, we catch any access to _default_manager
@@ -174,5 +178,3 @@ class PolymorphicModelBase(ModelBase):
 
         return super(PolymorphicModelBase, self).__getattribute__(name)
 
-
-

polymorphic/polymorphic_model.py

@@ -114,48 +114,74 @@ class PolymorphicModel(models.Model):
         if real_model == self.__class__: return self
         return real_model.objects.get(pk=self.pk)
 
-    # hack: a small patch to Django would be a better solution.
-    # For base model back reference fields (like basemodel_ptr),
-    # Django definitely must =not= use our polymorphic manager/queryset.
-    # For now, we catch objects attribute access here and handle back reference fields manually.
-    # This problem is triggered by delete(), like here:
-    # django.db.models.base._collect_sub_objects: parent_obj = getattr(self, link.name)
-    # TODO: investigate Django how this can be avoided
-    def __getattribute__(self, name):
-        if not name.startswith('__'):         # do not intercept __class__ etc.
 
-            # for efficiency: create a dict containing all model attribute names we need to intercept
-            # (do this only once and store the result into self.__class__.inheritance_relation_fields_dict)
-            if not self.__class__.__dict__.get('inheritance_relation_fields_dict', None):
+    def __init__(self, * args, ** kwargs):
+        """Replace Django's inheritance accessors member functions for our model
+        (self.__class__) with our own versions.
+        We monkey patch them until a patch can be added to Django
+        (which would probably be very small and make all of this obsolete).
 
-                def add_if_regular_sub_or_super_class(model, as_ptr, result):
-                    if ( issubclass(model, models.Model) and model != models.Model
-                        and model != self.__class__ and model != PolymorphicModel):
+        If we have inheritance of the form ModelA -> ModelB ->ModelC then
+        Django creates accessors like this:
+        - ModelA: modelb
+        - ModelB: modela_ptr, modelb, modelc
+        - ModelC: modela_ptr, modelb, modelb_ptr, modelc
+
+        These accessors allow Django (and everyone else) to travel up and down
+        the inheritance tree for the db object at hand.
+
+        The original Django accessors use our polymorphic manager.
+        But they should not. So we replace them with our own accessors that use
+        our appropriate base_objects manager.
+        """
+        super(PolymorphicModel, self).__init__(*args, ** kwargs)
+        if self.__class__.polymorphic_super_sub_accessors_replaced: return
+        self.__class__.polymorphic_super_sub_accessors_replaced = True
+
+        def create_accessor_function_for_model(model):
+            def accessor_function(self):
+                attr = model.base_objects.get(pk=self.pk)
+                return attr
+            return accessor_function
+
+        subclasses_and_superclasses_accessors = self.get_inheritance_relation_fields_and_models()
+        #print '###',self.__class__.__name__,subclasses_and_superclasses_accessors
+
+        from django.db.models.fields.related import SingleRelatedObjectDescriptor, ReverseSingleRelatedObjectDescriptor
+
+        for name,model in subclasses_and_superclasses_accessors.iteritems():
+            orig_accessor = getattr(self.__class__, name, None)
+            if type(orig_accessor) in [SingleRelatedObjectDescriptor,ReverseSingleRelatedObjectDescriptor]:
+                #print 'replacing',name, orig_accessor
+                setattr(self.__class__, name, property(create_accessor_function_for_model(model)) )
+
+    def get_inheritance_relation_fields_and_models(self):
+        """helper function for __init__:
+        determine names of all Django inheritance accessor member functions for type(self)"""
+
+        def add_model(model, as_ptr, result):
             name = model.__name__.lower()
             if as_ptr: name+='_ptr'
             result[name] = model
 
-                def add_all_base_models(model, result):
-                    add_if_regular_sub_or_super_class(model, True, result)
-                    for b in model.__bases__:
-                        add_all_base_models(b, result)
+        def add_model_if_regular(model, as_ptr, result):
+            if ( issubclass(model, models.Model) and model != models.Model
+                and model != self.__class__
+                and model != PolymorphicModel ):
+                add_model(model,as_ptr,result)
 
-                def add_sub_models(model, result):
+        def add_all_super_models(model, result):
+            add_model_if_regular(model, True, result)
+            for b in model.__bases__:
+                add_all_super_models(b, result)
+
+        def add_all_sub_models(model, result):
             for b in model.__subclasses__():
-                        add_if_regular_sub_or_super_class(b, False, result)
+                add_model_if_regular(b, False, result)
 
         result = {}
-                add_all_base_models(self.__class__,result)
-                add_sub_models(self.__class__,result)
-                #print '##',self.__class__.__name__,' - ',result
-                self.__class__.inheritance_relation_fields_dict = result
+        add_all_super_models(self.__class__,result)
+        add_all_sub_models(self.__class__,result)
+        return result
 
-            model = self.__class__.inheritance_relation_fields_dict.get(name, None)
-            if model:
-                id = super(PolymorphicModel, self).__getattribute__('id')
-                attr = model.base_objects.get(id=id)
-                #print '---',self.__class__.__name__,name
-                return attr
-
-        return super(PolymorphicModel, self).__getattribute__(name)
         

polymorphic/tests.py

@@ -249,8 +249,8 @@ __test__ = {"doctest": """
 
 >>> settings.DEBUG=True
 
->>> get_version()
-'1.0 rc1'
+#>>> get_version()
+#'1.0 rc1'
 
 
 ### simple inheritance