Introducing the Python Datastore API

In the Python API for the App Engine datastore, Python objects represent datastore entities. The class of the object corresponds to the entity’s kind, where the name of the class is the name of the kind. You define kinds by creating classes that extend one of the provided base classes.

Each attribute of the object corresponds with a property of the entity. To create a new entity in the datastore, you call the class constructor, set attributes on the object, then call a method to save it. To update an existing entity, you call a method that returns the object for the entity (such as via a query), modify its attributes, and then save it.

Example 5-1 defines a class named Book to represent entities of the kind Book. It creates an object of this class by calling the class constructor, and then sets several property values. Finally, it calls the put() method to save the new entity to the datastore. The entity does not exist in the datastore until it is put() for the first time.