Hi Nick,
I have something like this:
class Foo(db.Model):
name = db.StringProperty()
...
class Bar(db.Model):
foo = db.ReferenceProperty(Foo, collection_name='bars')
foo_name = db.StringProperty()
class Baz(db.Model):
foo = db.ReferenceProperty(Foo, collection_name='bazs')
foo_name = db.StringProperty()
I have added a hook in my application which calls a post_put() method on all
instances that are put() into the Datastore (after they are put, obviously).
In the post_put() of a Foo entity, I want to get all "reverse" referenced
Bar and Baz entities, and update their foo_name with the Foo entity's name.
However, I only need to update the Bar and Baz entities who's foo_name value
!= the Foo entity's name. So I could do something like:
class Foo(db.Model):
...
def post_put():
for collection_name in ('bars', 'bazs'):
q = getattr(self, collection_name)
q.filter('foo_name !=', self.name)
# Fetch, then update.....
This works fine, except I need to add a new index each time I do this, since
"q" has two filters, one equality (an implied filter('foo =', self)) and one
inequality.
Instead, I would like to get the Model class associated with each
collection_name and just add one inequality filter, ie:
class Foo(db.Model):
...
def post_put():
for collection_name in ('bars', 'bazs'):
model_class = self.get_model_class_for_collection(collection_name)
q = model_class.all().filter('foo_name !=', self.name)
# Fetch, then update.....
def get_model_class_for_collection(collection_name):
q = getattr(self, collection_name)
return q.model_class() # This is the Query method I want
This way I do not need to create a new index each time I do this.
Can you suggest a similar no-new-index way of doing this?
I also thought about doing this (only get_model_class_for_collection() has
changed):
class Foo(db.Model):
...
def post_put():
for collection_name in ('bars','bazs'):
model_class = self.get_model_class_for_collection(collection_name)
q = model_class.all().filter('foo_name !=', self.name)
# Fetch, then update.....
def get_model_class_for_collection(collection_name):
q = getattr(self, collection_name)
entity = g.get()
return entity.__class__
Forgetting about the extra Datastore get() required, the method above could
cause problems when it comes to PolyModel entities, because (correct me if I
am wrong) when PolyModel entities come back from the Datastore they are
instances of the deepest subclass in the entity's inheritance chain, so
returning entity.__class__ (in the last line above) will limit the results
of the query (with the single inequality filter) to entity's of the original
entity's PolyModel subclass. I hope that makes sense.
Nick, I would love to get your ideas on this. Also, I'm no Python expert so
if I'm overcomplicating things please let me know.
Cheers,
Nick
On 19 February 2010 22:50, Nick Johnson (Google) <nick.john...@google.com>wrote:
> Hi Nickolas,
>
> There's no public interface for this. Why do you need to do it?
>
> -Nick Johnson
>
> On Fri, Feb 19, 2010 at 11:28 AM, Nickolas Daskalou <n...@daskalou.com>wrote:
>
>> Is there an "official" way to get the Model class from a Query instance? I
>> had a look through the online docs and couldn't find anything.
>>
>> In the SDK code however, the Model class of a Query instance can be
>> retrieved from the _model_class attribute of the Query instance, eg:
>>
>> q = MyModel.all()
>> ....
>> model_class = q._model_class # == MyModel
>>
>> I don't really want to do it this way because since this is not documented
>> anywhere, I'm afraid that this implementation may change in the future.
>>
>> --
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>
>
>
> --
> Nick Johnson, Developer Programs Engineer, App Engine
> Google Ireland Ltd. :: Registered in Dublin, Ireland, Registration Number:
> 368047
>
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