Hi everyone!
I have a simple "Invoices" class with a "Number" attribute that has to
be filled in by the application when the user saves an invoice. There
are some constraints:
1) the application is a (thin) client-server one, so whatever
determines the number must look out for collisions
2) Invoices has a "version" attribute too, so I can't use a simple
DBMS-level autoincrementing field
I'm trying to build this using a custom Type that would kick in every
time an invoice gets saved. Whenever process_bind_param is called with
a None value, it will call a singleton of some sort to determine the
number and avoid collisions. Is this a decent solution?
Anyway, I'm having a problem.. Here's my custom Type:
----------------
class AutoIncrement(types.TypeDecorator):
impl = types.Unicode
def copy(self):
return AutoIncrement()
def process_bind_param(self, value, dialect):
if not value:
# Must find next autoincrement value
value = "1" # Test value :)
return value
----------------
My problem right now is that when I save an Invoice and AutoIncrement
sets "1" as value for its number, the Invoice instance *doesn't* get
updated with the new number.. Is this expected? Am I missing
something?
Many thanks for your time!
(SQLA 0.5.3 on Python 2.6, using postgreSQL 8.3)
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