Ian Lewis • 12/27/2009

Writing Schema migrations for App Engine using the Mapper Class and the deferred Library

This technical article addresses the challenges of performing schema migrations on Google App Engine's datastore, where altering object keys requires reprocessing large datasets. It explains how to leverage the task queue and the deferred library for background processing. The core of the article provides an updated, corrected version of a Mapper class to safely and efficiently handle large-scale data updates and deletions, overcoming bugs found in the original implementation.

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#Datastore #Appengine #Schema Migration