Hi Jeff,
Thanks for the response. It's exactly the requirement (for the DRY
principal or whatever) to have houses for both parents and children.
It makes sense to select houses for either parents or children.
I am not sure how the collection_name back reference is implemented or
if it would even work if collection_name was callable. If it could
work, it might be something like:
class Parent(polymodel.PolyModel):
house = db.ReferenceProperty(House, collection_name=some_func)
class Child(Parent):
pass
and some how have some_func vary from when Parent is parsed and when
Child is parsed, so it returns 'parents' and 'children' respectively.
I actually have no idea how this could work. :)
Cheers,
Oliver
On May 26, 3:44 pm, "Jeff S (Google)" <j...@google.com> wrote:
> Hi Oliver,
>
> Great suggestion and I want to make sure I understand the proposal. It
> sounds like you would like the House model to have a parents back
> reference and also a children back reference? How would the children
> collection be given a collection name?
>
> Here's some sample code to make this easier to follow:
>
> from google.appengine.ext import db
> from google.appengine.ext.db import polymodel
>
> class House(db.Model):
> address = db.IntegerProperty()
>
> class Parent(polymodel.PolyModel):
> house = db.ReferenceProperty(House, collection_name='parents')
>
> class Child(Parent):
> pass
>
> h1 = House(address=5).put()
> Parent(house=h1).put()
> Child(house=h1).put()
> Parent(house=h1).put()
> h1 = db.get(h1)
> h1.parents.fetch(5)
>
> With the above code, the h1 House instance has 3 entities in its
> parents back reference, 2 Parent instances and 1 Child instance.
> Instead you would like only the 2 Parent classes to appear in
> h1.parents? If that's the case, then you can do something like this
> instead:
>
> class Parent(polymodel.PolyModel):
> house = db.ReferenceProperty(House, collection_name='parents')
>
> class Child(Parent):
> home = db.ReferenceProperty(House, collection_name='children')
>
> h1 = House(address=5).put()
> Parent(house=h1).put()
> Child(home=h1).put()
> Parent(house=h1).put()
> h1 = db.get(h1)
> h1.parents.fetch(5)
> h1.children.fetch(5)
>
> I'm guessing the above would be OK if it is acceptable that the
> Child's reference to House is called 'home' instead of the parent
> classes 'house'.
>
> Thank you,
>
> Jeff
>
> On May 22, 11:19 am, Oliver Zheng <goo...@oliverzheng.com> wrote:
>
> > I'm trying to create a hierchy of kinds, the obvious reason of which
> > is that kinds can share model fields. However, for
> > ReferenceProperties, collection_name is fixed to when the model field
> > is declared in the model class. If this is declared in the parent
> > class, then all the children will have this collection name, which is
> > likely inaccurate:
>
> > class Parent(PolyModel):
> > house = db.ReferenceProperty(House, collection_name='parents')
>
> > class Child(Parent):
> > pass
>
> > House won't have a back reference to children in particular. And since
> > for PolyModels, fields cannot be overriden by children classes, Child
> > can't have its own house field.
>
> > This problem could be solved if collection_name was callable, so that
> > the children class could return its own collection name. Is there
> > plans for this?
>
>
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