How to commit related models - ember.js

Question

I'm working with ember-pre4 and ember-data rev 11.
Models:
A = DS.Model.extend({
//some other fields
b: DS.hasMany('B')
})
B = DS.Model.extend({
//some other fields
a: DS.hasOne('A')
})
In my router I create an instance of model A and create an instance of model B and connect them. They both don't have server-side id. Something like this:
var a = A.createRecord();
b = B.createRecord();
b.set('a', a)
a.get('b').addObject(b)
When I want to save those models I make:
a.transaction.commit()
And I expected to see:
Save a with empty b // []
After saving a pass a's id into b and save b
After saving b refetch a
But unfortunately ember does 2 request in parallel and a's request data is:
"{//some fields, b: [/url_to_b//]}" // we dont have b's id
b's request data is:
"{//some fields } // we dont have a's id
What is the best way to solve this problem, does new ember have a default solution for my situation or I should do all stuff manually?

Answer 1

Solution:
I wrapped createRecord function in waitForParents function:
waitForParents:function (record, callback, context) {
var observers = new Em.Set();
record.eachRelationship(function (name, meta) {
var relationship = get(record, name);
if (meta.kind === 'belongsTo' && relationship && get(relationship, 'isNew')) {
var observer = function () {
relationship.removeObserver('id', context, observer);
observers.remove(name);
finish();
};
relationship.addObserver('id', context, observer);
observers.add(name);
}
});
finish();
function finish() {
if (observers.length === 0) {
callback.call(context);
}
}
},
createRecord:function (store, type, record) {
this.waitForParents(record, function () {
// createRecord code here
}
}