Fun with GAE: using key_name as PK?

I want to insert new entities programatically as well as manually. For 开发者_高级运维this I was thinking about using key_name to uniquely identify an entity.

The problem is that I don't know how to get the model to generate a new unique key name when I create the entity.

On the other hand, I cannot create the ID (which is unique across data store) manually.

How can I do "create unique key name if provided value is None"?

Thanks for your help!

If you really need a string id (as opposed to an automatically assigned integer id), you could use a random string generator, or unique id generator like uuid.uuid4.

I don't really understand your question. If you want an automatically-generated key name, just leave out the key when you instantiate the object - one will be automatically assigned when you call put().

If most of the time you want your entities to have automatically assigned ids, then just go around creating your entities (without passing a key or key_name), the key will be auto-assigned and your entities will have .key().id() available.

If sometimes you need to assign the numeric ids manually, then you can reserve a block of ids so that AppEngine will never auto-assign them, and then you can use an id from this reserved range whenever you want to assign an id to a known entity. To assign an id to an entity you create a Key for that entity:

# reserve ids 4000 to 5000 for use manually on the Customer entity
db.allocate_id_range(db.Key.from_path('Customer',1),4000,5000)

# manualy create a customer with id 4501
bob = Customer(key=db.Key.from_path('Customer',4501), name='bob')
bob.put()