JDO + RequestFactory - entity versioning - google-app-engine

Question

I was trying to set-up a really trivial RequestFactory example, but I failed. I persist entities in to my datastore just find, however when trying to pull them out again, i get a
com.google.web.bindery.requestfactory.server.UnexpectedException: The persisted entity with id aglub19hcHBfaWRyCgsSBFVzZXIYBAw has a null version
So first of all this is my JPO annotated entity class. At the end you find to static function for RequestFactory to call, and a non-static member function which will become an InstanceRequest.
package com.test.server;
import java.util.List;
import javax.jdo.PersistenceManager;
import javax.jdo.annotations.Column;
import javax.jdo.annotations.Extension;
import javax.jdo.annotations.IdGeneratorStrategy;
import javax.jdo.annotations.IdentityType;
import javax.jdo.annotations.PersistenceCapable;
import javax.jdo.annotations.Persistent;
import javax.jdo.annotations.PrimaryKey;
import javax.jdo.annotations.Version;
import javax.jdo.annotations.VersionStrategy;
#PersistenceCapable(identityType = IdentityType.APPLICATION)
#Version(strategy = VersionStrategy.VERSION_NUMBER, column = "VERSION", extensions = { #Extension(vendorName = "datanucleus", key = "field-name", value = "version") })
public class User {
public User() {
}
public User(String name) {
this.name = name;
}
#PrimaryKey
#Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
#Extension(vendorName = "datanucleus", key = "gae.encoded-pk", value = "true")
private String id;
#Persistent
#Column(name = "version")
private Integer version;
#Persistent
private String name;
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public Integer getVersion() {
return version;
}
public void setVersion(Integer version) {
this.version = version;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public static final PersistenceManager persistenceManager() {
return PMF.get().getPersistenceManager();
}
#SuppressWarnings("unchecked")
public static List<User> findAllUsers() {
PersistenceManager pm = persistenceManager();
try {
String query = "SELECT FROM " + User.class.getName();
List<User> objects = (List<User>) pm.newQuery(query).execute();
objects.size(); // This is the workaround to retrieve all objects
return objects;
} finally {
pm.close();
}
}
public static User findUser(String id) {
PersistenceManager pm = persistenceManager();
try {
User u = pm.getObjectById(User.class, id);
return u;
} finally {
pm.close();
}
}
public void persist() {
PersistenceManager pm = persistenceManager();
try {
pm.makePersistent(this);
} finally {
pm.close();
}
}
}
The RequestFactory interface itself is really simple
package com.test.shared;
import com.google.web.bindery.requestfactory.shared.RequestFactory;
public interface UserOrderRequestFactory extends RequestFactory {
UserRequest userRequest();
}
so is the corresponding RequestContext
package com.test.shared;
import java.util.List;
import com.google.web.bindery.requestfactory.shared.InstanceRequest;
import com.google.web.bindery.requestfactory.shared.RequestContext;
import com.google.web.bindery.requestfactory.shared.Service;
import com.google.web.bindery.requestfactory.shared.Request;
import com.test.server.User;
#Service(User.class)
public interface UserRequest extends RequestContext {
Request<List<UserProxy>> findAllUsers();
InstanceRequest<UserProxy, Void> persist();
}
Here is the proxy of user for the client side
package com.test.shared;
import com.google.web.bindery.requestfactory.shared.EntityProxy;
import com.google.web.bindery.requestfactory.shared.EntityProxyId;
import com.google.web.bindery.requestfactory.shared.ProxyFor;
#ProxyFor(com.test.server.User.class)
public interface UserProxy extends EntityProxy {
EntityProxyId<UserProxy> stableId();
String getName();
void setName(String name);
}
and finally my onModuleLoad() which first persists a user and then gets a list of all users.
public void onModuleLoad() {
final EventBus eventBus = new SimpleEventBus();
requestFactory = GWT.create(UserOrderRequestFactory.class);
requestFactory.initialize(eventBus);
UserRequest userRequest = requestFactory.userRequest();
UserProxy user = userRequest.create(UserProxy.class);
user.setName("Luigi");
userRequest.persist().using(user).fire( new Receiver<Void>()
{
#Override
public void onSuccess(Void arg0)
{
GWT.log("User persisted.");
}
});
userRequest = requestFactory.userRequest();
Request<List<UserProxy>> findAllUsersRequest = userRequest.findAllUsers();
findAllUsersRequest.fire( new Receiver<List<UserProxy>>() {
#Override
public void onSuccess(List<UserProxy> list) {
for(UserProxy u: list) {
GWT.log(u.getName());
}
}
});
Any input is welcome. I would be happy to receive any advice on this.
Thank you in advance.

Answer 1

While JPA seems to do this automatically it seems to be my job to advance the version counter in JDO. I added the following code to my persist routine in User.java
// JPA #Version does this automatically, but JDO #Version is not working like that. Not sure why.
if (version == null) {
version = 0l;
}
version++;

Answer 2

I am not sure if it matters but the #Version column = "VERSION" does not match the #Column(name = "version").
However GAE does not really have 'columns' as such and you can just ignore them by removing the column = "" and the #Column.
See http://gae-java-persistence.blogspot.com.au/2009/10/optimistic-locking-with-version.html