I noticed an issue that - well, I honestly don't know whether to call
it a "bug" or not. I need to talk it out with somebody who
understands SQLA better.
When I retrieve an instance, then alter its attributes by manipulating
its __dict__, the instance doesn't get "dirtied", and the changes
won't be sent to the database when I flush the session.
My reason: I've got a program that retrieves rows from a database,
then applies a bunch of operations (stored as text) to each row, sort
of like so:
operations = [
'if firstname in ('Bob', 'Sam') then performance_review = "lazy"',
'if department == "IT" then vacation_days += 10']
for operation in operations:
for employee in employees.select():
exec(operation, employee.__dict__)
By passing the __dict__ to exec, each operation works directly on the
fields of each instance. But afterward, my session's .dirty remains
empty, and the changes don't get flushed.
I can work around the problem pretty easily, like this:
exec(operation, employee.__dict__)
employee._state['modified'] = True
That change to ._state normally happens in
InstrumentedAttribute.__set__ in sqlalchemy/orm/attributes.py (line
263), which gets called for "instance.attribute = newvalue", but not
for "instance.__dict__['attribute'] = newvalue".
I'm wondering if I should just sit on this workaround personally, or
dig into figuring out how to modify SQLA so it will always work for
__dict__ manipulation.
So - is direct manipulation of the __dict__ something that SQLA should
support, or would that fall in the realm of "you are getting weird on
us, you're on your own"? I guess that double-underscore sort of
implies "you're on your own", but __dict__ manipulation doesn't seem
overly exotic in practice.
Thanks,
- Catherine
http://catherinedevlin.blogspot.com
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