Breezejs does not trigger knockout update if relation is deleted

Question

I am playing with breezejs, and I have the problem that a computed knockout observable is not getting updated. Let me explain with a made-up example:

I have an entity (Session) with a one-to-many relation to another entity (Speaker). I fetch all Sessions with all related Speakers using the expand function in breezejs:

breeze.EntityQuery.from('Sessions').expand('Speakers');

On the breeze manager I am configuring a computed observable in the entity constructor:

var mgr = new breeze.EntityManager(config.remoteServiceName);
mgr.metadataStore.registerEntityTypeCtor('Session', null, sessionInitializer);

function sessionInitializer(session) {
    session.hasOldSpeaker = ko.computed(function () {
        for (var i = 0; i < session.speakers.length; i++) {
            var speaker = session.speakers[i];

            if (speaker.age() > 40) {
                return true;
            }
        }

        return false;
    });
}

I can then listen on this observable in the view:

<span data-bind="visible: session.hasOldSpeaker">....</span>

Now I have a button that can remove the old speaker from a session, so that we no longer have any old speakers. I make a normal ajax request to do this, because it is not just updating the database, some other work must also be done, so I don't think I can do this through breeze. Anyway, after the work is done I tell breeze to refresh the entity:

var refreshQuery = breeze.EntityQuery.fromEntities(session).expand('Speakers');
manager.executeQuery(refreshQuery);

The refresh seems to work OK, as the list of related speakers for the session is now empty - but the view does not update to hide the span above.

Does anybody know why the computed binding is not updated?

If I refresh the page, then it correctly hides the span.

Update

After testing with marking all speakers for a session as deleted using Breeze's entityAspect.setDeleted, I can see that the knockout binding works as expected. So I think the problem is in the way I refresh the session entity. Maybe someone have a better way of using breeze like this? - It is not just a database update, I need to kick off some Work on the server as well. What is the best way to do this with Breeze?

PW Kad PW Kad · Accepted Answer · 2013-06-21T14:28:19

Based on what I can tell it doesn't look like your computed is letting Knockout know to subscribe to the hasOldSpeaker property, only to the age of the speaker (which doesn't change if you change the session's speaker)

Because you are computing the hasOldSpeaker property and only subscribing to the age property, by simply changing the session or the speaker it won't subscribe to anything besides the speakers age, from what I can tell. Wrapping your computed in an if statement should properly subscribe to the session's speaker property.

function sessionInitializer(session) {
    session.hasOldSpeaker = ko.computed(function () {
        if (session.speaker()) {
            for (var i = 0; i < session.speakers.length; i++) {
                var speaker = session.speakers[i];

                if (speaker.age() > 40) {
                    return true;
                }
                else { return false; }
            }
        }

        return false;
    });
}

Breezejs does not trigger knockout update if relation is deleted

1 Answers