c...@your solution, PK! Since db.PropertiedClass is not documented in the official docs, I'm assuming there's a chance that its implemented could change in future releases, and possibly break your code yeah?
Can someone from Google please comment on whether db.PropertiedClass is "concrete" enough to be able to use it in such a manner as described in PK's article? Nick On 5 March 2010 20:18, Nickolas Daskalou <n...@daskalou.com> wrote: > Thanks PK, I'll check it out now. > > Nick > > > On 5 March 2010 19:41, PK <p...@gae123.com> wrote: > >> Hi Nick, >> >> I have been using the pattern described by Rafe very successfully in >> my app. Regarding the problem you are desribing I have written up how >> I solved the problem here: >> >> http://www.gae123.com/articles/tds/model-mixin.html >> >> Read the whole page for the details or just scroll to the bottom for >> the solution that has worked for me. >> >> PK >> http://www.gae123.com >> >> On Mar 4, 10:22 pm, Nickolas Daskalou <n...@daskalou.com> wrote: >> > Using non-Model mix-ins worked a treat. Thanks again Rafe. >> > >> > There is one small problem I'm hoping you can help me with (again). It's >> not >> > a show-stopper because I can work around it, however I'm hoping you'd >> know >> > of a nicer way to do this. Note that it's not only specific to >> PolyModel, >> > but to db.Model as well. >> > >> > The problem is with adding extra db.* properties to these mix-ins (so >> that >> > all subclasses that use the mix-in get these extra properties stored in >> the >> > Datastore). >> > >> > Let's say I change the CoolFeature mix-in to this: >> > >> > class CoolFeature(object): >> > >> > * cool_name = db.StringProperty()* >> > >> > def put(self): >> > self.cool_name = 'Cool ' + self.name >> > super(CoolFeature, self).put() >> > >> > class MyModel(CoolFeature,db.Model): >> > >> > name = db.StringProperty() >> > >> > If I then create an instance of MyModel and try put()'ing it to the >> > Datastore: >> > >> > mm = MyModel(name='blah') >> > mm.put() >> > >> > I get this error: >> > >> > Traceback (most recent call last): >> > ... >> > File >> > >> "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/ext/db/__init__.py", >> > line 473, in __set__ >> > setattr(model_instance, self._attr_name(), value) >> > File >> > >> "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/ext/db/__init__.py", >> > line 588, in _attr_name >> > return '_' + self.name >> > TypeError: cannot concatenate 'str' and 'NoneType' objects >> > >> > This error occurs both on the dev and production servers. >> > >> > Upon further investigation, the error occurs because the name property >> of >> > the underlying Property superclass of the cool_name property instance is >> > None. So I then changed the bold line above to: >> > >> > cool_name = db.StringProperty(name='cool_name') >> > >> > This got rid of the error being raised, however the cool_name property >> was >> > not saved to the Datastore (only the name property was). >> > >> > The workaround is to add the property cool_name to each >> > CoolFeaturesubclass. So it's not terribly bad, but if you know of a >> > better way to >> > accomplish what I'm trying to do, I'd love to hear it. >> > >> > Cheers, >> > >> > Nick >> > >> > On 5 March 2010 12:40, Nickolas Daskalou <n...@daskalou.com> wrote: >> > >> > >> > >> > > Thanks for your reply Rafe. Using non-Model mix-ins seems like the way >> to >> > > go. >> > >> > > As with many App Engine developers, my Python experience is equivalent >> to >> > > my App Engine experience, so I appreciated the Python lesson ;) >> > >> > > Nick >> > >> > > On 5 March 2010 08:52, Rafe <slobberch...@gmail.com> wrote: >> > >> > >> There is currently no proper way to do "re-root" a polymodel the way >> > >> you are describing. However, there may be a solution for your >> > >> particular problem. I don't know enough about your actual >> > >> implementation however you might get away with simply doing a non- >> > >> Model based mix-in. So, write your memcache utility class AS IF it >> > >> inherits from PolyModel, but don't actually allow it to do so. Like >> > >> this: >> > >> > >> class CoolFeature(object): >> > >> > >> def put(self): >> > >> ... clear memcache ... >> > >> super(CoolFeature, self).put() >> > >> > >> Now define your root class: >> > >> > >> class MyModel(CoolFeature, polymodel.PolyModel): >> > >> ... >> > >> > >> Here comes the Python lesson, so forgive me if you already know all >> > >> this ;) >> > >> > >> The key is that you use 'super' correctly and that you have >> > >> CoolFeature be the first class your model class inherits from. >> > >> 'super' allows you to traverse your objects functionality correctly >> > >> according to the python "method resolution order". You can see this >> > >> order by for any class by studying MyModel.__mro__. This indicates >> > >> the order which calls to super will traverse your class definitions. >> > >> If you do: >> > >> > >> class A(object): >> > >> > >> def p(self): >> > >> print 'A' >> > >> > >> class B(object): >> > >> > >> def p(self): >> > >> print 'B' >> > >> super(B, self).p() >> > >> > >> class C(B, A): >> > >> > >> def p(self): >> > >> print 'C' >> > >> super(C, self).p() >> > >> > >> ...calling C().p() will print: >> > >> > >> C >> > >> B >> > >> A >> > >> > >> You should be able to implement whatever functionality you need this >> > >> way. Let me know if there are issues with doing that. >> > >> > >> On Mar 3, 7:40 pm, Nickolas Daskalou <n...@daskalou.com> wrote: >> > >> > I should state that I can set the entity kind that's saved in the >> > >> > Datastore by adding a kind() method on my "real" models, however >> the >> > >> > class list property of the saved entities still includes the >> "special" >> > >> > PolyModel subclass in it, and I'm not sure if that's a bad thing or >> > >> > not. >> > >> > >> > On Mar 4, 2:16 pm, Nickolas Daskalou <n...@daskalou.com> wrote: >> > >> > >> > > I've been trying to create a "special" subclass of PolyModel >> (that >> > >> does cool >> > >> > > stuff like update Memcache after an entity put()) which my >> polymodel >> > >> models >> > >> > > can inherit from (instead of inheriting from >> db.polymodel.PolyModel). >> > >> > >> > > This has the nasty side effect though of making that "special" >> > >> subclass of >> > >> > > PolyModel the root class for my polymodel models. >> > >> > >> > > Is there a way around this? >> > >> > >> > > Eg. Telling db.polymodel.PolyModel to NOT include the first >> direct >> > >> subclass >> > >> > > in the class hierarchy that is saved to the Datastore? Or writing >> my >> > >> own >> > >> > > PolyModel by basically copying db.polymodel and changing code >> where >> > >> > > appropriate? >> > >> > >> > > Appreciate any help. >> > >> > >> > > Nick >> > >> > >> -- >> > >> You received this message because you are subscribed to the Google >> Groups >> > >> "Google App Engine" group. >> > >> To post to this group, send email to >> google-appeng...@googlegroups.com. >> > >> To unsubscribe from this group, send email to >> > >> google-appengine+unsubscr...@googlegroups.com<google-appengine%2bunsubscr...@googlegroups.com> >> <google-appengine%2bunsubscrib...@googlegroups.com> >> > >> . >> > >> For more options, visit this group at >> > >>http://groups.google.com/group/google-appengine?hl=en.- Hide quoted >> text - >> > >> > - Show quoted text - >> >> -- >> You received this message because you are subscribed to the Google Groups >> "Google App Engine" group. >> To post to this group, send email to google-appeng...@googlegroups.com. >> To unsubscribe from this group, send email to >> google-appengine+unsubscr...@googlegroups.com<google-appengine%2bunsubscr...@googlegroups.com> >> . >> For more options, visit this group at >> http://groups.google.com/group/google-appengine?hl=en. >> >> > -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. 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