Hi Adam, The "Fake"Mixin order is very important, unless all "Fake"Mixins are inherited before the class inherits from db.Model it will throw an error. So as long as you make sure you have db.Model at the end of your inheritances it should be fine.
regards, Moritz On Thu, Nov 20, 2008 at 12:20 AM, Adam <[EMAIL PROTECTED]> wrote: > > I'm fairly sure that I tried just this very solution before giving up > on it because it continued to throw exceptions. Since you say that > this worked for you, I'll try it again and make sure that I am > matching this pattern as closely as possible. > > On Nov 19, 10:36 am, "Moritz Angermann" <[EMAIL PROTECTED]> > wrote: >> Ohh, after some thinking, how about this: >> Basically This is a Coutable Mixin wich replaces the .count() method >> on objects by caching the value in a seperate table. >> code below or (http://dpaste.com/hold/92118/for more convinient reading) >> [ tried this in the SDK console] >> >> kindest regards, >> Moritz >> >> PS: it is important to have the mixin order... e.g. all db.Model >> deriving classes before the db.Model class. >> >> from google.appengine.ext import db >> >> class _Counter(db.Model): >> """ >> some helper class, to keep track >> of the actual amount of elements >> """ >> count = db.IntegerProperty(default=0) >> >> class Countable(db.Model): >> """ >> the ``mixin'' to make an object have >> a cheap ``.count()'' method >> """ >> >> def count(klass): >> return _Counter.get_or_insert('class:%s' % klass.__name__).count >> count = classmethod(count) >> def put(self,*args,**kwargs): >> if not self.is_saved(): >> counter = _Counter.get_or_insert('class:%s' % self.__class__.__name__) >> counter.count += 1 >> counter.put() >> super(Countable, self).put(*args,**kwargs) >> >> def delete(self, *args, **kwargs): >> counter = _Counter.get_by_key_name('class:%s' % self.__class__.__name__) >> if not counter is None: >> counter.count -= 1 >> counter.put() >> super(Countable, self).delete(*args,**kwargs) >> >> class Test(Countable, db.Model): >> name = db.StringProperty() >> >> print "set up" >> print "======" >> print " installing 10 entities in Test model..." >> for i in range(10): >> Test(name='item %d' % i).put() >> print "test" >> print "====" >> print " Test.count() yields ", Test.count() >> print " deleting two entities" >> for e in Test.all().fetch(2): >> e.delete() >> print " Test.count() yields ", Test.count() >> print "tear down" >> print "=========" >> print " deleting all items from Test model..." >> for e in Test.all(): >> e.delete() >> print " deleting all items from _Counter model..." >> for e in _Counter.all(): >> e.delete() >> >> On Wed, Nov 19, 2008 at 11:18 PM, Robin B <[EMAIL PROTECTED]> wrote: >> >> > Have you tried having ModelMixin inherit from PropertiedClass >> > directly: >> >> > class ModelMixin(PropertiedClass): >> > pass >> >> > class Commentable(): >> > __metaclass__ = ModelMixin >> >> > I am using something similar without error. >> >> > Robin >> >> > On Nov 19, 8:07 am, Adam <[EMAIL PROTECTED]> wrote: >> >> Not that anyone cares, but the metaclass approach did not work, as >> >> Python doesn't want to have two non-identical metaclasses in an >> >> inheritance chain. Or something. >> >> >> On Nov 18, 10:42 am, Adam <[EMAIL PROTECTED]> wrote: >> >> >> > It just occurred to me that this solution could be made much easier by >> >> > using a simple, small metaclass (which, it is worth noting, I totally >> >> > copped from GAE's PropertiedClass metaclass): >> >> >> > class ModelMixin(type): >> >> > def __init__(cls, name, bases, dct): >> >> > super(PropertiedClass, cls).__init__(name, bases, dct) >> >> >> > for attr_name in dct.keys(): >> >> > attr = dct[attr_name] >> >> > if isinstance(attr, Property): >> >> > cls._properties[attr_name] = attr >> >> >> > class Commentable(): >> >> > __metaclass__ = ModelMixin >> >> >> > comments_counter = db.IntegerProperty(required=True, default=0) >> >> >> > Bada-bing. Now, the ugly nonsense of creating the _properties dict >> >> > and assigning to it is gone. > > > --~--~---------~--~----~------------~-------~--~----~ 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-appengine@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en -~----------~----~----~----~------~----~------~--~---
