hi mike! there are a couple things going on here.
first, your all().filter() example returns no results because there's
no space between ancestor and =, so it thinks you're filtering on a
property named 'ancestor='. the docs note that you need a space before
the filter operator:
http://code.google.com/appengine/docs/datastore/queryclass.html#Query_filter
. also see http://code.google.com/p/googleappengine/issues/detail?id=688
. try adding a space.
as for the GQL queries, the catch is the confusion between your
ancestor parent and the ancestor query feature. specifically, ANCESTOR
is a reserved keyword in GQL, and it always expects a valid, non-null
key as its argument, which is why you get the GQL errors.
On Mar 28, 2:40 am, Mike <i...@michaelwirth.me> wrote:
> Hello,
>
> I'm playing around with AppEngine and seem to get around many of its
> restrictions after some time. But now I'm stuck on this issue for
> several hours:
> I have a tree of groups. Every group has several sub-groups etc. The
> whole thing is stitched together with a SelfReferenceProperty called
> ancestor, so every group knows its parent.
> However, the top group(s) have a <null> value for the field ancestor
> (which I can see in the Data Viewer). In the group viewer I want to
> show the top level groups if no id is provided. I have tried to query
> for my groups with a null value the following ways, without success:
>
> groups = Group.all().filter('ancestor=', None) -> no results, no
> error
>
> groups = db.GqlQuery("SELECT * FROM Group WHERE ancestor IS :1", db.Key
> (None)) -> error: Incomplete key
>
> groups = db.GqlQuery("SELECT * FROM Group WHERE ancestor <") -> (I
> found this in this group) error: Expected IS after ancestor
>
> Does anyone know how a (Self)ReferenceProperty can be queried for the
> null value? It should be possible because the value is not missing, it
> is just set to null. I am also open to other solutions for saving a
> tree of objects in the datastore, which should be quite a common
> problem.
>
> Thank you for your help!
> Mike
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