Can I add a promise/unmaterialized record to a hasMany while I wait for it to be retrieved? - ember-data

Question

Back in the unversioned Ember Data days (e.g. "rev 12" maybe) I'm pretty sure you could do this:
var comment = App.Comment.find(42); // Already exists, but not yet loaded...
post.get('comments').addObject(comment);
Because App.Comment.find(42) would return an App.Comment object, albeit one with no fields populated except it's ID. (I don't remember the details of how you'd then save the App.Post--i.e. if you could or couldn't save it until the comment object was completely loaded…I never got that far.)
Why this was neat is that if your template rendered post.comments, a new row/div would appear immediately that could check isLoaded to display a loading indicator and show instantly that a new record was attached while waiting for the record's data to load. This is/was a selling point of Ember/Ember Data, and one I really like.
But this doesn't work now in 1.0.0-beta.2 beta.4 beta.5:
var comment = controller.get('store').find('comment', 42);
post.get('comments').addObject(comment); // Fails
Because controller.get('store').find('comment', 42) returns a promise, and if I try to add it to the hasMany it complains that I can only add App.Comment objects to the relationship.
Is it still possible to do something like this, so that my template which renders the comments immediately updates with a new record, but asynchronously populates its data?
(Please ignore that it doesn't make sense to add an already existing comment to a post--using the ubiquitous example scenario is easier than posting all my model code. Thanks!)

Answer 1

Okay, I came up with at least one way that does it:
var comment = controller.get('store').find('comment', 42);
var inFlightRecord = controller.get('store').getById('comment', 42);
controller.get('comments').addObject(inFlightRecord);
To be safer, maybe:
var comment = controller.get('store').find('comment', 42);
var inFlightRecord = controller.get('store').getById('comment', 42);
if(inFlightRecord){ // should be null if it isn't in the store
controller.get('comments').addObject(inFlightRecord);
} else {
// add a then block to the promise to make sure it gets added later
}
It seems that getById returns the "unloaded" object like we used to get from App.Comment.find(42), and the object still has an isLoaded property you can check to show loading status in your template.
I'm not sure if this is supposed to be supported behavior that I can rely on going forward (I suppose arguably nothing is, until 1.0 release), but it seems to work. I even checked that the object returned by getById === the object fulfilled in the promise. So this seems to be a good solution.
Anyone see a problem with this, or have a better way?