Google App Engine Datastore - OneToMany update operation fails due to bug in JPA datanucleus
NOTICE Google Cloud Platform documentation states that JPA and JDO should not be used with Datastore ( see: JPA overview , JDO overview ) Developers should consider using low level Datastore API (for simple cases) or use Objectify library which is specifically created for Datastore. This issue has been reported to GAE issue tracker: https://code.google.com/p/googleappengine/issues/detail?id=11995 Code to reproduce this issue is available HERE When this issue occurs GAE SDK Version: 1.9.17 and higher (probably lower versions too - not tested) DataNucleus JPA: 3.1.3, 3.1.4 DataNucleus-Appengine: 2.1.1, 2.1.2 When you use JPA to persist your domain objects and you try to update OneToMany relation by removing old objects and adding new objects. Ex. "User" class has "items" field - classic one to many relation as shown below: User has many Items (OneToMany relation represented by "User.items" field) Why it