On Tuesday 02 September 2008 22:50:09 Michael Bayer wrote: > On Sep 2, 2008, at 3:06 PM, Sam Magister wrote: > > Hi, > > > > I'm using joined table inheritance much like the example given > > here: > > http://www.sqlalchemy.org/docs/05/mappers.html#advdatamapping_map > >per_inheritance_joined > > > > Additionally, in the employees table, I would like an > > update_timestamp column of type DateTime: > > > > Column('update_timestamp', DateTime, > > onupdate=datetime.datetime.now()) > > Theres a common mistake here. Either have onupdate set to > datetime.datetime.now (no parenthesis), or set it to func.now() to > allow the database's own time function to be used. > > > I was just wondering if there was an easy way to get around this > > issue without using MapperExtensions. Previously I was using > > MapperExtensions and overriding the before_update method which > > works since it looks for updates in the entire instance, not just > > that table. This way works fine, but I like the cleanness of not > > needing MapperExtensions. > > the MapperExtension approach can be made more clean by creating a > generic one: > > 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. A future release may include decorators which > accomplish a similar result. this can be useful, especialy if some attempt is made to combine all the (non-overlapping) funcs into one MapExt - and not chain many simple ones. even in the plain usage, some optimisation over the given list of mapExts can be done - to avoid walking the list at each event - e.g. converting the list of MapExt-dict-of-handlers into dict of { method:list-of-handlers } -- but i guess this is more suitable for a fancy 'try this' section in the docs - the speedup may or may not be noticeable.
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