Weird, I was _just_ discussing this with a colleague at our office. If you want a really hard check and are willing to pay some overhead for it, AND you can't use the key_name approach that Robert suggests which is the best solution, you can use a technique like this: http://squeeville.com/2009/01/30/add-a-unique-constraint-to-google-app-engine/
We've typically used this for a User entity where we need a unique email address, but we don't want to drive the email address into the key_name because email addresses change. j On Jul 20, 9:42 pm, cwaldbieser <[email protected]> wrote: > I have 3 models: A customer account, a service, and a model that > represents a customer's subscription to the service. The subscription > is essentially: > > class Subscription(db.Model): > customer = db.ReferenceProperty(Customer) > service = db.ReferenceProperty(Service) > > I have a user interface that allows creating or cancelling a > customer's subscription. I want to be able to create a subscription > only if an existing subscription does not already exist. I thought > that a transaction might be the key, but I can't do a query in > transaction unless it is by key or an ancestor query. So I am not > sure what to do. > > Any thoughts? > > Thanks, > Carl -- 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.
