Hi,
I have created an Identity Mapper for my website - which is as
follows:
class IdentityMap(object):
def __getattr__(self, name):
if not hasattr(self, name):
setattr(self, name, {})
return getattr(self, name)
MAP = IdentityMap()
class MapManager(models.Manager):
def get(self, *args, **kwargs):
if kwargs.has_key('mapname'):
parm = kwargs.pop('mapname')
dval = getattr(MAP, self.model.__name__)
if not dval.has_key(parm):
dval[parm] = super(MapManager, self).get(*args,
**kwargs)
return dval[parm]
else:
return super(MapManager, self).get(*args, **kwargs)
#Model which is overriden by all models
class BaseModel(models.Model):
objects = MapManager()
class Meta:
abstract = True
#--------------------------------------------------------------------------------
#
Everytime a get is issued (due to lazy loading I did not implement the
same for filter), it first checks whether the given mapname is already
stored inside MAP, and if not only then will it issue a proper get.
Mapname is given by the user - he can give any unique name to it.
Now, I wanted to do it for all models. Since User is part of
django.auth, I overrode User too as given below.
from django.contrib.auth.models import User, UserManager
class MyUserManager(UserManager):
def get(self, *args, **kwargs):
if kwargs.has_key('mapname'):
parm = kwargs.pop('mapname')
dval = getattr(MAP, self.model.__name__)
if not dval.has_key(parm):
dval[parm] = super(MyUserManager, self).get(*args,
**kwargs)
return dval[parm]
else:
return super(MyUserManager, self).get(*args, **kwargs)
class MyUser(User):
objects = MyUserManager()
class Meta:
abstract = True
#--------------------------------------------------------------------------------
#
But when I issued a get on MyUser, it is failing with the following
error
File "C:\django\My\..\My\test\test.py", line 164, in UserData
data.save(form)
File "C:\django\My\..\My\test\models.py", line 361, in save
self.user = MyUser.objects.find(form.cleaned_data['user'],
username=form.cleaned_data['user'])
File "C:\django\My\..\My\test\models.py", line 93, in find
dval[parm] = self.get(*args, **kwargs)
File "C:\Python24\Lib\site-packages\django\db\models\manager.py",
line 93, in get
return self.get_query_set().get(*args, **kwargs)
File "C:\Python24\Lib\site-packages\django\db\models\query.py", line
337, in get
num = len(clone)
File "C:\Python24\Lib\site-packages\django\db\models\query.py", line
161, in __len__
self._result_cache = list(self.iterator())
File "C:\Python24\Lib\site-packages\django\db\models\query.py", line
281, in iterator
for row in self.query.results_iter():
File "C:\Python24\Lib\site-packages\django\db\models\sql\query.py",
line 254, in results_iter
for rows in self.execute_sql(MULTI):
File "C:\Python24\Lib\site-packages\django\db\models\sql\query.py",
line 2011, in execute_sql
sql, params = self.as_sql()
File "C:\Python24\Lib\site-packages\django\db\models\sql\query.py",
line 362, in as_sql
out_cols = self.get_columns(with_col_aliases)
File "C:\Python24\Lib\site-packages\django\db\models\sql\query.py",
line 588, in get_columns
col_aliases)
File "C:\Python24\Lib\site-packages\django\db\models\sql\query.py",
line 633, in get_default_columns
root_pk = opts.pk.column
AttributeError: 'NoneType' object has no attribute 'column'
I even tried changing the metaclass, but it does not seem to have any
effect.
Can someone help me out?
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