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Failed to obtain a generated Id with my programme. GWT

I am working on a client-server project in GWT and after the user fills a form, I would like to update my database and eventually create new datas.
For that, I create a "sensor" and the system link with which it is associated. But, the "sensor" is associated with a sensor Family too and I must create the link in my table sensorFamilySensorFamilyLink but I do not managed.
Indeed, here is my code for the creation of the sensor and the link:
#Override
public void updateSensor(SystemDTO system, SensorDTO sensorDTO, String sensorFamName) {
Sensor sensor = null;
SensorFamily sensorFam = null;
if(sensorDTO.getId() <0) {
sensor = new Sensor();
sensor.fillFromDTO(sensorDTO);
sensor.create();
}
else {
sensor = Sensor.queryById(sensorDTO.getId());
sensor.fillFromDTO(sensorDTO);
sensor.update();
}
sensorFam = SensorFamily.queryByName(sensorFamName);
// Creation of the link between sensor and sensorFamily.
SensorFamilySensorLink linksensor = null;
if (!linkFam.isEmpty()) {
linksensor = linkFam.get(0); // We take the first one because there is only one.
}
if(linksensor == null) { // creation of a sensor
//List<SensorFamilySensorLink> liste = SensorFamilySensorLink.query();
linksensor = new SensorFamilySensorLink();
linksensor.setSensorId(sensor.getId());
linksensor.setSensorFamilyId(sensorFam.getId());
linksensor.create();
}
else {
linksensor.setSensorFamilyId(sensorFam.getId());
linksensor.update();
}
Whereas the update works, the creation of the link does not work. Here is my code for the method "create":
#PersistenceCapable(identityType = IdentityType.APPLICATION, detachable = "true")
public class SensorFamilySensorLink {
/** The id. */
#PrimaryKey
#Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
private long id;
/** The associated sensor id. */
#Persistent
private long sensorId;
/** The associated sensorFamily id. */
#Persistent
private long sensorFamilyId;
/**
* Create.
*/
public void create() {
PersistenceManager pm = PMF.getManager();
Transaction tx = pm.currentTransaction();
try {
tx.begin();
pm.makePersistent(this);
tx.commit();
} catch(Exception e) {
} finally {
if (tx.isActive()) {
tx.rollback(); // Error occurred so rollback the PM transaction
}
}
pm.close();
}
After debuggind, the problem comes from the generation if the IDs to use the SQL method INSERT in the table. THe generated id does not work when I am doing:
pm.makePersistent(this);
Is someone can say to me what I have forgotten because I have been searching for two days and I do not how to solve the problem? Besides, I use the same code for creating the sensor link with the system and the family link and it is working for the first one.
If you need more information, do not hesitate to ask me. Thanks in advance.

Removing/deleting from google datastore using endpoints, illegal arguement exception, delete with non-zero content length not supported

I'm trying to delete objects from the datastore (using cloud endpoints)
I know the connection is valid because I'm pulling/inserting objects with no problem
However when I try to delete using various approaches I get the same exception
java.lang.illegalArgumentException:DELETE with non-zero content length is not supported
approach 1(using the raw datastore service and the key I stored when inserting the item):
#ApiMethod(name = "removeRPurchase")
public RPurchase removeRPurchase(RPurchase purchase) {
NamespaceManager.set(purchase.getAccount());
DatastoreService d=DatastoreServiceFactory.getDatastoreService();
Key k=KeyFactory.stringToKey(purchase.getKeyrep());
try {
d.delete(k);
} catch (Exception e) {
e.printStackTrace();
purchase=null;
}
return purchase;
}
Approach 2
#ApiMethod(name = "removeRPurchase")
public RPurchase removeRPurchase(RPurchase purchase) {
NamespaceManager.set(purchase.getAccount());
Key k=KeyFactory.stringToKey(purchase.getKeyrep());
EntityManager mgr = getEntityManager();
RPurchase removed=null;
try {
RPurchase rpurchase = mgr.find(RPurchase.class, k);
mgr.remove(rpurchase);
removed=rpurchase;
} finally {
mgr.close();
}
return removed;
}
Ive also tried various variations with the entity manager and the Id, but all with the same exception
The object that i've passed in does contain the namespace in the account, and it does contain the 'KeytoString' of the key associated with the object
the endpoint is called as it should in an AsyncTask endpoint.removeRPurchase(p).execute();
Any help suggestions are appreciated

Make your API method a POST method like this:
#ApiMethod(name = "removeRPurchase" path = "remove_r_purchase", httpMethod = ApiMethod.HttpMethod.POST)
public RPurchase removeRPurchase(RPurchase purchase) {
NamespaceManager.set(purchase.getAccount());
DatastoreService d=DatastoreServiceFactory.getDatastoreService();
Key k=KeyFactory.stringToKey(purchase.getKeyrep());
try {
d.delete(k);
} catch (Exception e) {
e.printStackTrace();
purchase=null;
}
return purchase;
}
I had the same problem because I was using httpMethod = ApiMethod.HttpMethod.DELETE. The error it gives is correct. Simply change it to a POST and do whatever you want inside that API method like delete entities, return entities, etc.

How about trying out the following :
#ApiMethod(
name = "removeRPurchase",
httpMethod = HttpMethod.DELETE
)
public void removeRPurchase(#Named("id") String id) {
//Now take the id and plugin in your datastore code to retrieve / delete
}

Oracle Berkeley DB Java Edition - Secondary key unicity

I have a simple entity class and it is supposed to include unique names on it.
#Entity
class Package {
#PrimaryKey(sequence = "ID")
public Long id;
#SecondaryKey(relate = Relationship.ONE_TO_ONE)
public String name;
private Package() {}
public Package(String name) { this.name = name; }
#Override
public String toString() { return id + " : " + name; }
}
I want to use deferred writing option because of extensive modification. Here is the test i tried and its output.
final String dbfilename = "test01";
new File(dbfilename).mkdirs();
EnvironmentConfig config = new EnvironmentConfig().setAllowCreate(true);
Environment environment = new Environment(new File(dbfilename), config);
StoreConfig storeConfig = new StoreConfig().setAllowCreate(true).setDeferredWrite(true);
EntityStore store = new EntityStore(environment, "", storeConfig);
PrimaryIndex<Long, Package> primaryIndex = store.getPrimaryIndex(Long.class, Package.class);
try {
primaryIndex.put(new Package("package01")); // will be put.
primaryIndex.put(new Package("package01")); // throws exception.
} catch (UniqueConstraintException ex) {
System.out.println(ex.getMessage());
}
store.sync(); // flush them all
// expecting to find one element
SortedMap<Long,Package> sortedMap = primaryIndex.sortedMap();
for (Package entity : sortedMap.values()) {
System.out.println(entity);
}
Output
(JE 5.0.73) Unique secondary key is already present
1 : package01
2 : package01
So my question is that even if it throws exception while putting second package, why does it lists two packages. Any way to avoid this without using transactions?
Thanks.

java google app engine get entity by key

I have a problem using GAEJ and JDO for storing the data.
This is what I'm working with:
class Usuari.java:
#PrimaryKey
#Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
private Key key;
#Persistent
private String email;
#Persistent
private String rol="";
class DBUtils.java:
I've tried with two ways of doing the delete operation:
// This method removes a record from the database using its unique Key
public static boolean eliminar(Key k) throws Exception {
PersistenceManager pm = PMF.get().getPersistenceManager();
String kind;
Long id;
kind = k.getKind();
id = k.getId();
try {
if (k.getKind().equals("Usuari")) {
Usuari u = (Usuari)pm.getObjectById(k);
pm.deletePersistent(u);
_log.log(Level.INFO, "Deleted an entity->kind: " + kind + " id: " + id);
}
return true;
} catch (Exception e) {
_log.log(Level.SEVERE, "Unable to delete an entity->kind: " + kind + " id: " + id);
System.err.println(e.getMessage());
throw e;
}
finally {
pm.close();
}
}
// This method removes a record from the database using its unique Key - too
public static void eliminar2(Key k) throws Exception {
PersistenceManager pm = PMF.get().getPersistenceManager();
javax.jdo.Transaction tx = pm.currentTransaction();
try
{
tx.begin();
if (k.getKind().equals("Usuari")) {
Usuari u = (Usuari) pm.getObjectById(k);
pm.deletePersistent(u);
}
tx.commit();
}
catch (Exception e)
{
if (tx.isActive())
{
tx.rollback();
}
throw e;
}
}
I'm able to create new instances of some class "Usuari" but I can't delete them.
Everytime I call "eliminar" or "eliminar2" methods I get a "No such object" as result of trying to fetch it. I've checked manually and I see the object exists in my admin panel, with its ID and KIND, so I don't know what am I doing wrong.
Any help would be much appreciated.

PM.getObjectById does not take in a Key object, as per the JDO spec. It takes in an identity object, the same type as you would get from pm.getObjectId(obj); suggest you glance through the JDO spec. No doubt if you inspected what is returned from this method you would see that it can't find an object with that 'identity' because a Key is not an identity. You can also do
pm.getObjectById(Usuari.class, key);
which is shown very clearly in GAE documentation.
Still don't get why users are putting #Persistent on every field virtually every type is default persistent; only leads to making code more unreadable.

google app engine: problem getting objects from datastore in a task

My application constructs a Parent object in a static factory, along with it's predetermined Children, and then starts up tasks to run some computation on the Children, like so:
public static Parent make(User owner, List<Integer> data, int size) {
Parent result = new Parent(owner,data,size);
PersistenceManager pm = PersistenceSource.get();
Transaction tx = pm.currentTransaction();
try {
tx.begin();
result = pm.makePersistent(result);
for (int i=0; i<size; pm.makePersistent(new Child(result,i++)));
pm.close();
tx.commit();
} finally {
if (tx.isActive()) { tx.rollback(); result=null; }
}
if (result!=null) {
Queue q = QueueFactory.getDefaultQueue();
for (Child c : result.getChild()) {
q.add(url("/task/child").param("key", KeyFactory.keyToString(c.getKey())).method(Method.PUT));
}
}
pm.close();
return result;
}
however in the actual task
public void doPut(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
PersistenceManager pm = PersistenceSource.get();
Child c = pm.getObjectById(Child.class, KeyFactory.stringToKey(request.getParameter("key"))); //...
It dies trying to find the object:
Could not retrieve entity of kind Child with key Child(24)
org.datanucleus.exceptions.NucleusObjectNotFoundException: Could not retrieve entity of kind Child with key Child(24)
Any insights? Also, if it matters, the Parent-child relationship is defined by the parent as a field in the child (hence construction with the parent as an arg).

After some plugging around, the following will work to properly retrieve the desired Child:
Key k = new KeyFactory
.Builder(Parent.class.getSimpleName(), Long.valueOf(request.getParameter("parent")))
.addChild(Child.class.getSimpleName(), Long.valueOf(request.getParameter("child")))
.getKey();
Child c = pm.getObjectById(Child.class, k);
I'm still a bit mystified coming from the non-DataStore world as to why the type + id is insufficient to fetch what I want. That seems equivalent to knowing table + primary key in SQL land, and the documentation seems to indicate that the key contains all the parent info, such that having it should be sufficient to do a direct pm.getObjectId(Child, KeyFactory./* etc */).

public Object retrieveChildByKey(Key parent, Class childClass, int idChild){
try{
pm = PMF.get().getPersistenceManager();
Key objectKey = KeyFactory.createKey(parent, childClass.getSimpleName(), idChild);
Object result = pm.getObjectById(childClass, objectKey);
return result;
}
catch (DatastoreTimeoutException ex) {
// Display a timeout-specific error page
message = "Timeout: An error has occurred: Was not possible to retrieve the Object";
System.out.println(message);
ex.printStackTrace();
}
catch(Exception ex){
message = "Timeout: An error has occurred: Was not possible to retrieve the Object";
System.out.println(message);
ex.printStackTrace();
}finally{
pm.close();
}
return null;
}