a synonym() is used so that your attributes are properly available in filter(). This functionality has been vastly improved in the current SVN trunk which resolves all the issues you outline above, and will be available in release 0.4.2. If you checkout the SVN trunk, you can do:

class MyAddress(object): def _set_email(self, email): self._email = email def _get_email(self): return self._email email = property(_get_email, _set_email)

mapper(MyAddress, addresses_table, properties = { 'email':synonym('_email', map_column=True) })

which automatically maps the column to the "_email" attribute, and also instruments the "email" property with the SQL comparator methods.