Recently, the App Engine team announced that they'd be pre-releasing SDKs for testing and feedback, before they go live in production. With the first prerelease, 1.3.1, a number of new features are included in the SDK. Today we'll discuss cursors - how they work, and what they're useful for.
Cursors are a feature that many people have been waiting for with bated breath. As well as making pagination easier, they also provide a way around the "1000 result limit" that many people feel (in some cases correctly) makes it harder to achieve what they want to do on App Engine.
When it comes to investigating new features, there are two really useful tools: An interactive console - such as that on http://localhost:8080/_ah/admin/, http://shell.appspot.com/ or the remote_api console - and the source code. Many people forget that as an Open Source project, the App Engine SDK code is all available - and easily browseable on code.google.com.
Our first stop is google/appengine/ext/db/__init__.py. Of interest here is the cursor() method, which starts on line 1600. As you can see, when called on a query that's already been ...