So "group.forum.threads.posts.fetch(10)" is exactly the type of thing
you need to be cautious of. That is actually doing a fetch to get the
forum, then another for threads, and lastly querying for ten posts.
That's a lot of datastore operations.
You might want to think about denormalizing your data structures so
that you can instad do something like:
Posts.all().filter('group', group.key()).order('-timestamp')
Robert
On Fri, Jan 27, 2012 at 01:36, ikalbeniz <[email protected]> wrote:
> ok.. in my case i have something like this..
>
> class ForumGroup(db.Model):
> name = db.StringProperty()
> description = db.StringProperty(multiline=True)
> created_at = db.DateTimeProperty(auto_now_add=True)
>
> class Forum(db.Model):
> name = db.StringProperty()
> description = db.StringProperty(multiline=True)
> group = db.ReferenceProperty(ForumGroup,collection_name='forums')
> created_at = db.DateTimeProperty(auto_now_add=True)
>
> Forum has a reference property group that references to ForumGroup so
> now ForumGroup object has a 'forums' property that is a Query
> object..
>
> i thought that when i got a ForumGroup doing get_by_id()
> simultaneously GAE made the query to get 'forums' object and so i got
> so many read quota..
>
> then i have other DB objects referenced so i can do
>
> group = ForumGroup().get_by_id(x)
>
> last_post_on_forum = group.forum.threads.posts.fetch(10)
>
>
>
> On 27 ene, 08:01, Robert Kluin <[email protected]> wrote:
>> Hi,
>> When you access those reference properties they are fetched by key.
>> Unfortunately this will happen serially, which will significantly
>> impact your performance. You're not going to avoid the read
>> operations without changing your schema, but you can at least improve
>> the performance by doing a batch fetch on all those referenced
>> entities. One way to do this would look something like:
>>
>> class SomeThing(db.Model):
>> ref_prop = db.ReferenceProperty()
>>
>> @property
>> def ref_prop_key(self):
>> return SomeThing.ref_prop.get_value_for_datastore(self)
>>
>> thing = db.get(some_thing_key)
>> other, entities = db.get([thing.ref_prop_key, thing.another_ref_prop_key])
>>
>> This trick is to then *never* directly touch thing.ref_prop because
>> it will fetch the entity again.
>>
>> Robert
>>
>>
>>
>>
>>
>>
>>
>> On Thu, Jan 26, 2012 at 07:30, ikalbeniz <[email protected]> wrote:
>> > Hi,
>>
>> > I have developed a forum where i have structured the database using
>> > ReferenceProperties to link forum groups, forums, threads, posts and
>> > users.. so a group (db.model object) has N forums that have N threads
>> > with N posts..
>>
>> > I have a problem with the Datastore Read Operations Quota and i think
>> > than can be because when i get a Group object GAE gives me all tree
>> > structure so with one get_by_id i have lots of Datastore Read
>> > Operations..
>>
>> > Can someone confirm that this is ok? How an i avoid GAE do this so if
>> > i only want to show Group properties values so i dont need to acces
>> > all forums belongs to the group..
>>
>> > thanks.
>>
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