Class update detection

[Axium Computer Services]

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

[Lars Heuer]

Re: Class update detection

Hi Axium,

[...][color=blue]
> 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[/color]
[...]

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

[Miki Tebeka]

Re: Class update detection

Hello Steven,
[color=blue]
> 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?[/color]
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__(sel f, k, v):
if k in ("a", "b"):
self.dirty = 1
self.__dict__[k] = v[color=blue][color=green]
>> c = C(1,2)[color=darkred]
>>> c.dirty[/color][/color][/color]
0[color=blue][color=green][color=darkred]
>>> c.a = 10
>>> c.a[/color][/color][/color]
10[color=blue][color=green][color=darkred]
>>> c.dirty[/color][/color][/color]
1[color=blue][color=green][color=darkred]
>>>[/color][/color][/color]

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