It seems that the unique constraint is not natively supported in GAE, although one can enforce unique check before putting an object to store.

But that was in January 2009, what about now? Can I specify unique constraint on a column during schema creation? i.e.

class Account(db.Model):
  name = db.StringProperty()
  email = db.StringProperty() as unique # something like this
  @classmethod
  def create(cls, name, email):
    a = Account(name=name, email=email)
    a.put()
    return a