> That's not a great answer, but in the meantime, you might want to take
> a look at the lazy instantiation in the GIS branch[1]. That code isn't
> exactly what you want, but it might help get you started on a
> descriptor-based approach to do what you're asking for until there's a
> proper solution.
Thanks Marty - that was exactly what I was looking for. Using a proxy
with descriptors solved my problem - what a nifty, sneaky little
trick!
I had some difficulty determining the context of the __set__ calls -
on loading from the db, the inbound value is the encrypted db value
(which needs to be encrypted only then), or due to a user changing the
value (in clear text - in which case the setter should not decrypt the
value) - and therefore the flag.
Here's my take on it:
class CharEncryptProxy(object):
def __init__(self, field):
self._field = field
self._decrypted = False
def __get__(self, obj, type=None):
return obj.__dict__[self._field.attname]
def __set__(self, obj, value):
# only decrypt first time if set by db
if (not self._decrypted) and (value != ''):
obj.__dict__[self._field.attname] =
self._field._decrypt(value)
else:
obj.__dict__[self._field.attname] = value
self._decrypted = True
class CharEncryptField(models.CharField):
def _encrypt(self, value):
if value is not None:
value = ''.join([chr(ord(char)+1) for char in str(value)])
return value
def _decrypt(self, value):
if value is not None:
value = ''.join([chr(ord(char)-1) for char in str(value)])
return value
def get_internal_type(self):
return "CharField"
def get_db_prep_save(self, value):
value = self._encrypt(value)
return super(CharEncryptField,
self).get_db_prep_save(value)
def contribute_to_class(self, cls, name):
super(CharEncryptField, self).contribute_to_class(cls, name)
# override with proxy
setattr(cls, self.attname, CharEncryptProxy(self))
Works like a charm - thanks again for putting me on the right track!
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