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
>
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--
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
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