You should balance the needs of querying for children against updating the
parent - if you are checking for the lack of children much more than you are
actually updating parents, it will be way cheaper to implement a boolean
that denotes whether or not the parent has children. This isn't a relational
database, and thinking non-relationally (away from normalization) will yield
many performance benefits.
On Tue, May 25, 2010 at 10:50 AM, App Engine N00B <
vivek.securitywiz...@gmail.com> wrote:
> Hi!
>
> I have many models:
>
> class Parent (db.Model) :
> data = db.StringProperty()
>
>
> class Child1 (db.Model) :
> parent = db.ReferenceProperty(Parent)
> childData = db.StringProperty()
>
> class Child2 (db.Model) :
> parent = db.ReferenceProperty(Parent)
> childData2 = db.StringProperty()
>
> class Child3 (db.Model) :
> parent = db.ReferenceProperty(Parent)
> childData3 = db.StringProperty()
>
>
>
> I want a query which can give me a list of all parents which do not
> have a child yet. How do i do it?
>
> I do not want to maintain an identifier in the Parent model for each
> of the children as I want to add new child models very often.
>
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--
Ikai Lan
Developer Programs Engineer, Google App Engine
Blog: http://googleappengine.blogspot.com
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