Google App Engine Versioning in the Datastore

Question

Google App Engine has the concept of app versions. i.e., you can have multiple versions of your app running concurrently and accessible at different subdomains. For instance: http://1.my-app-name.appspot.com, http://2.my-app-name.appspot.com.

What aspects of the app are actually "versioned" by this? Is it only the Python + Static files codebase? Does the datastore have the concept of "versions"? If not, then what happens when I update the definition of a Google App Engine model?

Thanks!

Answer 1

Correct, app version refers only to your uploaded files. Both versions use with the same datastore.

Note that the datastore itself is schema-less. Each entity is an independent collection of key/value pairs. Two entities of the same kind don't have to share the same set of properties, or property types. db.Model provides an ORM abstraction around the datastore, but doesn't define or enforce any kind of global schema.

While the datstore isn't versioned, it does support namespacing. If you want a new datastore segment for each major version of your app, you can do this:

import os
from google.appengine.api import namespace_manager

namespace_manager.set_namespace(os.environ['CURRENT_VERSION_ID'])

Answer 2

Datastore has no concept of versions.

When you update a model definition, any entities you create in the future will be of the new type, and the old ones will be of the old type. This frequently leads to runtime errors if your code is not aware of these changes.