如何在Google App Engine _ah / api / explorer中创建com.google.appengine.api.datastore.Key对象？

Question

I have a GAE JDO annotated object:

@PersistenceCapable
public class HelloGreeting {

  @PrimaryKey
  @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
  private Key id;

  @Persistent
  private String message;

  ... constructors, getters, setters
}

and my own endpoint:

public HelloGreeting update(HelloGreeting helloGreeting)
        throws NotFoundException {
    PersistenceManager pm = PMF.get().getPersistenceManager();
    try {
        pm.getObjectById(HelloGreeting.class, helloGreeting.getId());
        ... some logic
    } finally {
        pm.close();
    }
    return helloGreeting;
}

where I would like to send from frontend or from the Google App Engine _ah/api/explorer the helloGreeting object.

When I create one using pm.makePersistent(helloGreeting); , then the api explorer shows me something like this:

{
 "id": {
   "kind": "HelloGreeting",
   "appId": "project-id",
   "id": "5629499534213120",
   "complete": true
  },
"message": "some text"
}

I use then this JSON structure to call the update(HelloGreeting helloGreeting) method via the api explorer and I'm getting the following error:

java.lang.NullPointerException at com.google.appengine.api.datastore.Key.getAppId(Key.java:279)
...
...

... which was because of line pm.getObjectById(HelloGreeting.class, helloGreeting.getId()); in my update(HelloGreeting helloGreeting) method.

It seems like the private Key id field is not unmarshalled correctly. I tried it also with pm.getObjectById(HelloGreeting.class, helloGreeting.getId().getId()); but with no success.

Can somebody please tell me if this is even possible?

PS: I can't change the type of the id field from Key to Long (which works) because then I wouldn't use inner child object annotated with @PersistenceCapable .

Answer 1

我不确定您的情况，但我认为您可能需要编写自定义转换器来确保正确重构密钥。

Answer 2

I solved this with a bit nasty solution. This is my update() endpoint:

public HelloGreeting update(HelloGreeting helloGreeting)
        throws NotFoundException {
    PersistenceManager pm = PMF.get().getPersistenceManager();
    try {
        if(!containsGreeting(helloGreeting)) {
            throw new NotFoundException("not exists");
        }
        // persisting the helloGreeting with the new Key
        pm.makePersistent(helloGreeting);
    } finally {
        pm.close();
    }
    return helloGreeting;
}

private boolean containsGreeting(HelloGreeting helloGreeting) {
    PersistenceManager pm = PMF.get().getPersistenceManager();
    boolean contains = true;
    try {
        // here I'm creating a new Key from the helloGreeting
        Key key = KeyFactory.createKey(HelloGreeting.class.getSimpleName(), helloGreeting.getId().getId());
        // using the Key for a query
        pm.getObjectById(HelloGreeting.class, key);
        // and rewriting the old incorrect unmarshalled Key by the new one 
        helloGreeting.setId(key);
    } catch (javax.jdo.JDOObjectNotFoundException ex) {
        contains = false;
    } finally {
        pm.close();
    }
    return contains;
}

If somebody knows a better solution, I would appreciate it.