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copied!<p>I think the that i've found the solution. It seems that every endpoint generated by Google App Engine(GAE) framework has a simple method which check every time that someone is trying to insert or update and a persistant instance, so the fact was every time that i've tried to insert a new student using curl/json without specify de new id for the instance it displayed a error message like this one:</p> <pre><code> "error": { "message": javax.jdo.JDOFatalInternalException: The key value passed to construct a SingleFieldIdentity type \ class javax.jdo.identity.LongIdentity \ for class \ class com.alex.wserver.Student \ is null. \ nNestedThrowables: \ norg.datanucleus.exceptions.NucleusException: the key value passed to construct a SingleFieldIdentity type \ class javax.jdo.identity.LongIdentity \ for class \ class com.alex . wserver.Student \ is null. </code></pre> <hr> <p>so i've solve the problem editing my endpoint class by checking if the new object(sent by curl command and wrapped json format) has a not null id value before even check if the object has been stored before with this code:</p> <pre><code> if(student.getKey() != null){ if (containsStudent(student)) { throw new EntityExistsException("Object already exists"); } } mgr.makePersistent(student); </code></pre> <hr> <p>As far i haven't seen any documentation which can clarify that aspect for me. Also i add, i've spend a lot of time reading the documentation on <a href="https://developers.google.com/appengine/docs/java/datastore/jdo/dataclasses">GAE</a> before trying to figure out what's been happening.</p> <hr> <p>All that made me think that maybe just maybe the GAE documentation is not up to date or probably i havent search enough, so if someone know about. please let me know it and grow the common knowledge. thanks @DataNucleus.</p> <p><strong>NOTE:</strong> "This fork that i've made should not be taked as correct answer, it could be take you to unexpected behavior of your app."</p>

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