Question

I am not really sure where my problem lies, as I am experimenting in two areas that I don’t have much experience with: JPA and Futures (using Play! Framework’s Jobs and Promises).

I have the following bit of code, which I want to return a Meeting object, when one of the fields of this object has been given a value, by another thread from another HTTP request. Here is what I have:

    Promise<Meeting> meetingPromise = new Job<Meeting> () {
        @Override
        public Meeting doJobWithResult() throws Exception {
            Meeting meeting = Meeting.findById(id);
            while (meeting.bbbMeetingId == null) {
                Thread.sleep(1000);
                meeting = meeting.refresh();       // I tried each of these
                meeting = meeting.merge();      // lines but to no avail; I
                meeting = Meeting.findById(id); // get the same result
            }
            return meeting;
        }
    }.now();
    Meeting meeting = await(meetingPromise);

As I note in the comments, there are three lines in there, any one of which I think should allow me to refresh the contents of my object from the database. From the debugger, it seems that the many-to-one relationships are refreshed by these calls, but the single values are not.

My Meeting object extends Play! Framework’s Model, and for convenience, here is the refresh method:

/**
 * Refresh the entity state.
 */
public <T extends JPABase> T refresh() {
    em().refresh(this);
    return (T) this;
}

and the merge method:

/**
 * Merge this object to obtain a managed entity (usefull when the object comes from the Cache).
 */
public <T extends JPABase> T merge() {
    return (T) em().merge(this);
}

So, how can I refresh my model from the database?

Answer 1

So, I ended up cross-posting this question on the play-framework group, and I got an answer there. So, for the discussion, check out that thread.

In the interest of having the answer come up in a web search to anyone who has this problem in the future, here is what the code snippet that I pasted earlier looks like:

Promise<Meeting> meetingPromise = new Job<Meeting> () {         
    @Override
    public Meeting doJobWithResult() throws Exception {
        Meeting meeting = Meeting.findById(id);
        while (meeting.bbbMeetingId == null) {
            Thread.sleep(1000);
            if (JPA.isInsideTransaction()) {
                JPAPlugin.closeTx(false);
            }
            JPAPlugin.startTx(true);
            meeting = Meeting.findById(id);
            JPAPlugin.closeTx(false);
        }
        return meeting;
    }
}.now();
Meeting meeting = await(meetingPromise);

I am not using the @NoTransaction annotation, because that messes up some other code that checks if the request is coming from a valid user.