Waldemar,
It is not necessary to have a separate Property type for accessing a
model key without loading it from the datastore. You can instead:
class MyModel(db.Model):
my_reference = db.ReferenceProperty()
....
my_instance = MyModel.all().get()
MyModel.my_reference.get_value_for_datastore(my_instance)
On Sep 13, 4:36 am, Waldemar Kornewald <[EMAIL PROTECTED]> wrote:
> Hi Frank,
> I reordered your mail a little bit.
>
> On Sep 12, 9:26 pm, Frank <[EMAIL PROTECTED]> wrote:
>
> > And the most puzzling is that this is always the same 'oParent' 150
> > times, since I'm listing its children, so I would expect this
> >ReferencePropertyto be cached already.
>
> ReferencePropertyonly caches for a single model, but you have 150
> models, so every child will get() its parent.
>
> > of course I am not talking about accessing theReferenceProperty'sown
> > properties, I am only interested to see if it's None (and I tried with
> > both '==' and 'is'), and also getting its id
> > (self.oParent.key().id()), and doing one or the other gives the same
> > behavior.
>
> As soon as you access oParent it will result in a get().
> Unfortunately, you can't get the key of aReferencePropertywithout
> dereferencing it. Well, there is a hacky solution:
> if self._oParent is None:
> ...
> Note that most properties store their real value in
> "_<property_name>", but Google might change this any time, so I
> wouldn't use it in an important app.
>
> Instead, I'd suggest you either store the str(key) in a StringProperty
> and manually get() it or you use our KeyReferenceProperty from
> appenginepatch's snippet library. If your parent node model is
> ParentNode you could define this:
>
> parent_key = db.StringProperty()
> parent = KeyReferenceProperty('parent_key', ParentNode,
> use_key_name=False)
>
> The "parent_key" property will store the str(key) of the parent while
> the "parent" property allows to access the parent directly (like
> withReferenceProperty). So, in order to test whether it's None you would
> write:
> if self.parent_key is None:
> ...
> If you want to access the parent model instance you can just write
> self.parent. This separation between key and model instance also makes
> writing transactional code that has to pass around key_names a little
> bit easier.
>
> You can rip out the source
> here:http://trac-hg.assembla.com/appenginepatch/browser/ragendja/dbutils.py
>
> Alternatively, if you use Django you can integrate it with
> appenginepatch and get the whole snippet
> library:http://code.google.com/p/app-engine-patch/
> But then I'd suggest you fetch the most recent source from the
> repository because that contains a few additions like support for
> setting the key via the KeyReferenceProperty (self.parent =
> some_parent_object).
>
> Bye,
> Waldemar Kornewald
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