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I have a relational database that has several tables each more or less
translating to a python class and the fields of each table translating
into attributes of the python class. I have no problem creating an
instance of the class, running a query and filling the attributes. Then
this information will be accessible from a UI. The problem I am running
into is when the user is done working in the UI I need to determine if
any of the class attributes have been changed to I can issue an update
query to the database with the changes. Is there a generally accepted
method to do this? Is there some way to create a checksum of the class
attributes?

Any help would be much appreciated.

Thanks

Steven Potter

Hi Axium,

[...]
> this information will be accessible from a UI. The problem I am running
> into is when the user is done working in the UI I need to determine if
> any of the class attributes have been changed to I can issue an update
> query to the database with the changes. Is there a generally accepted
[...]

I.e. SQLObject (and other ORMs, too) does this job. If you update a
class attribute, it automatically updates the underlying DB tables.
http://sqlobject.org/


Best regards,
Lars

Hello Steven,

> I need to determine if
> any of the class attributes have been changed to I can issue an update
> query to the database with the changes. Is there a generally accepted
> method to do this? Is there some way to create a checksum of the class
> attributes?
Do you mean something in the lines of:
class C:
def __init__(self, a, b):
self.a, self.b = a, b
self.dirty = 0
def __setattr__(self, k, v):
if k in ("a", "b"):
self.dirty = 1
self.__dict__[k] = v
>> c = C(1,2)
>>> c.dirty
0
>>> c.a = 10
>>> c.a
10
>>> c.dirty
1
>>>

Another option is to generate a checksum (using md5 and str) on all the
attributes you're interested in at the end of __init__ and a function
`dirty' will compute this checksum and return 1 if it was changed.
Note that if you have nested objects this might be a problem.

HTH.
Miki