I'm trying to create a custom CharField that would encrypt a field's
contents before saving to the db, and conversely decrypt the field's
values from the db as it loads (using a public key).
I want to make sure that the contents of this field is encrypted in
the database, but decrypted whenever I work with the field in Django -
nice and transparent to all the developers. I could add a new
property to my model and have it decrypt the field, but this field's
been around for ages and I don't want to mod all the dependencies.
Sub-classing CharField seemed the obvious choice and encrypting on
save is easy - I simply override the Field's get_db_prep_save()
method.
But I can't find a post-load hook for decrypting the value as soon as
the field's value gets loaded from the db.
This is the part that works well - encrypting on save (silly
encryption algorithm permitting:)
class EncryptedCharField(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(EncryptedCharField, self).get_db_prep_save(value)
Does anyone have any idea how I could hook into and change the field's
value as soon as the value gets loaded from the db?
Where can I call my _decrypt() method from? I would like to call it
once - the moment the results from the Model's QuerySet are parsed and
the Model's field values populated.
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