Thanks Nick. The reason I use entity groups is not for any kind of performance reasons – I really need to make sure that the Parent entity is updated in combination with a Child entity being added, and the values being set are related to the order of entity insertions, so entity groups feel like the right thing to do to ensure data atomicity.
My only thought is that I'd rather add redundancy (by adding a ReferenceProperty that can be inferred from the key) than lose performance. If the performance difference is negligible however, I'd rather not add an unnecessary property. /Blixt On Jul 19, 1:21 pm, "Nick Johnson (Google)" <[email protected]> wrote: > Hi Blixt, > > > > > > On Mon, Jul 19, 2010 at 12:15 PM, Blixt <[email protected]> wrote: > > Imagine the following models: > > > class Parent(db.Model): > > name = db.StringProperty() > > count = db.IntegerProperty() > > > class Child(db.Model): > > number = db.IntegerProperty() > > value = db.StringProperty() > > > Whenever a new Child is added, it is added with a Parent as its parent > > entity in a transaction which also updates some values on the Parent. > > > My question is this: To get a list of children that belongs to a > > Parent, is it more efficient to add a ReferenceProperty to the Child > > model and filter by that, than it is to use the ancestor filter in > > queries? > > > To clarify in code: > > > # Using ancestor > > Child.all().ancestor(parent_key).fetch(10) > > # Using filter on a new ReferenceProperty called 'my_parent' > > Child.all().filter('my_parent', parent_key).fetch(10) > > These two should have roughly the same performance. > > Bear in mind, though, that if you don't need entity groups for transaction > purposes, you should avoid using ancestor relationships. Given that, the > second approach is a better one - just not for query performance reasons. > > -Nick Johnson > > > > > -- > > 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]<google-appengine%2Bunsubscrib > > [email protected]> > > . > > For more options, visit this group at > >http://groups.google.com/group/google-appengine?hl=en. > > -- > Nick Johnson, Developer Programs Engineer, App Engine Google Ireland Ltd. :: > Registered in Dublin, Ireland, Registration Number: 368047 > Google Ireland Ltd. :: Registered in Dublin, Ireland, Registration Number: > 368047 -- 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.
