On Dec 21, 2008, at 6:53 AM, Kless wrote:
>
> I'm trying to build a custom type [1] to manage the bcrypt hashes [2].
>
> ---------------
> from bcrypt_wrap import password
> from sqlalchemy import types
>
>
> class Bcrypt(types.TypeDecorator):
> """Stores a bcrypt hash of a password."""
> impl = types.String #(60)
> hasher = password.Password()
>
> def process_bind_param(self, value, dialect):
> return hasher.create(value)
> ---------------
>
> And I've any doubts:
>
> 1) Since that the hash length is always 60, is there that use the
> next?
> impl = types.String(60)
>
> 2) The bcryptWrap API [3] (line 53) lets call to 'create' with
> arguments 'cost' and 'admin' (boolean). Then,
>
> a) I would that the cost could be passed from the column definition,
> i.e.
> password = sqlalchemy.Column(types.Bcrypt, cost=12)
> or
> password = sqlalchemy.Column(types.Bcrypt(cost=12))
>
> b) This would be more hard, but I would to pass the 'admin' argument
> when an object is created
>
> u = model.User()
> u.login = u'foo'
> u.password = u'bar'
> u.admin = True
>
> And sou could be call:
> return hasher.create(value, admin=True)
>
the TypeDecorator's __init__ method just calls the impl class
immediately, so the best approach is like:
class Bcrypt(types.TypeDecorator):
"""Stores a bcrypt hash of a password."""
impl = types.String
hasher = password.Password()
def __init__(self, cost):
self.cost = cost
types.TypeDecorator.__init__(self, 60)
def process_bind_param(self, value, dialect):
return hasher.create(value)
then you can instantate like:
Column('foo', Bcrypt(cost=12))
For b, the type object and the ExecutionContext which ultimately calls
its process_bind_param method are unaware of the ORM or the ORM-
specific context in which its called during INSERT/UPDATE. If you
wanted to keep the logic within your type like that you'd have to
integrate to a thread-local variable that is configured within an ORM
plugin, something like:
hasher_status = threading.local()
class MyMapperExt(MapperExtension):
def before_insert(self, ...):
hasher_status.admin = instance.admin
def after_insert(self, ...)
del hasher_status.admin
mapper(MyClass, table, ext=MyMapperExt)
class Bcrypt(types.TypeDecorator):
...
def process_bind_param(self, value, dialect):
return hasher.create(value, getattr(hasher_status, 'admin',
False))
Alternatively, you could keep the logic within the ORM using either a
"valdiator" or a descriptor, as described at
http://www.sqlalchemy.org/docs/05/mappers.html#changing-attribute-behavior
. It depends on if you'd like your Bcrypt type to work with direct
SQL expression language use or not.
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