Question

I’ve made a guestbook application using Google App Engine(GAE):python and the client is running on iPhone.

It has ability to write messages on the board with nickname.
The entity has 3 fileds:

1. nickname
2. date
3. message

And I’m about to make another feature that user can post reply(or comment) on a message.

But to do this, I think there should a ‘primary key’ to the guestbook entity, so I can put some information about the reply on a message.

With that three fields, I can’t get just one message out of database.

I’m a newbie to database. Does database save some kind of index automatically? or is it has to be done by user?

And if it’s done automatically by database itself(or not), how can I get just one entity with the key??

And I want to get some advise about how to make reply feature generally also. Thanks to read.

Answer 1

Every entity has a key. If you don’t assign a key_name when you create the entity, part of the key is an automatically-assigned numeric ID. Properties other than long text fields are automatically indexed unless you specify otherwise.

To get an entity if you know the key, you simply do db.get(key). For the replies, you probably want to use a db.ReferenceProperty in the reply entity to point to the parent message; this will automatically create a backreference query in the message to get replies.