Well yes I could add a count property to the B objects, but I'm really trying to understand more about how ReferenceProperty works.
Nonetheless, there are a couple reasons I don't want to add a count property to the B objects: -- Every time I create or delete an A object, I would also have to make two additional datastore calls to read, modify, and write object B. -- And to make sure the counter stays in sync, I would need to use a datastore transaction for these operations. But right now, my A and B objects are not in the same entity group, which means (if I understand correctly) transactions are not supported. So I would have to do a full update to the existing datastore in order to add a reliable counter to object B. On Jun 21, 12:31 pm, Sylvain <[email protected]> wrote: > Could you add an int property that is updated with the len ? > So you only check this property ? > > On 21 juin, 17:51, johntray <[email protected]> wrote: > > > > > If I have two datastore object types, I'll call A and B, and A > > includes a ReferenceProperty to B, then objects of type B will have a > > back-reference property with default name a_set. Now if I just want > > the size of some B object's a_set, I could call len(a_set). To execute > > this, my understanding is that GAE will do a datastore query to > > retrieve the relevant A objects and pass them to the len() function. > > Since I don't need the A object contents, would it be more efficient > > to set up my own Query object and call Query.count() instead? --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Google App Engine" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en -~----------~----~----~----~------~----~------~--~---
