btw, using the "__before_update__" technique introduced some weird data
corruption issues for me when my class had PickleType datamembers. For
instance,
# Create the Foo class to map foos_table to
class Foo(object):
def __before_update__(self):
self.some_pickle_type
self.last_edit_date = datetime.now()
the sql update statement generated would set some_pickle_type to NULL, even
though I hadn't modified the datamember. This doesn't matter hugely to me at
the moment, because I no longer am using a table hierarchy, and hence don't
need to use __before_update__ anymore, but thought I would mention it in
case anyone else runs into it.
>>> sqlalchemy.__version__
'0.5.4p2'
On Mon, Mar 2, 2009 at 12:43 PM, John Fries <john.a.fr...@gmail.com> wrote:
> Thanks Michael! That should have been obvious to me, but for some reason I
> couldn't figure it out.
>
>
> On Mon, Mar 2, 2009 at 11:24 AM, Michael Bayer
> <mike...@zzzcomputing.com>wrote:
>
>>
>> On Mar 2, 2009, at 2:16 PM, John Fries wrote:
>>
>> Hi all,
>>
>> I am having a problem that is identical to the one mentioned last year on
>> this list:
>>
>> http://groups.google.com/group/sqlalchemy/browse_thread/thread/efd3993c94c8d162/37943cda02151f2b?lnk=gst&q=onupdate+inheritance#37943cda02151f2b
>>
>> I have Engineer and Manager tables that are inheriting from an Employee
>> table using joined table inheritance. When I update one of the child
>> tables, I want the last_edited timestamp column on the Employee table to be
>> updated as well, but it is not updating. Mr. Bayer proposes the following:
>>
>> """
>> from sqlalchemy.orm import mapper as _mapper
>> from sqlalchemy.orm import MapperExtension
>>
>> class MyExt(MapperExtension):
>> def before_update(self, mapper, connection, instance):
>> if hasattr(instance, '__before_update__'):
>> instance.__before_update__()
>>
>> def mapper(*args, **kw):
>> kw['extension'] = MyExt()
>> return _mapper(*args, **kw)
>> just hide that code away someplace, and then any instance which
>> defines a method called __before_update__() will have it called before
>> update.
>> """
>>
>> I've done that step, but I don't understand what the next step is. I
>> thought that I would have to implement a __before_update__ method on my
>> Engineer and Manager classes, which would then call some method on Employee
>> using super. However, when I update my Engineer, it doesn't even look like
>> the __before_update__ method is being called. So I conclude that I'm doing
>> it wrong. Which instances should implement a __before_update__ method?
>> What should the __before_update__ method do?
>>
>>
>> just implement def __before_update__() on your base Employee class. this
>> method should set the last_edited attribute to a new value (note you can set
>> it to "func.now()" to have a SQL function fire off). Engineer and Manager
>> will have the method automatically via class inheritance. Also make sure
>> you are using the modfied mapper() function to create your mappers.
>>
>>
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