Having trouble setting Ember objects to both contain references to each other - ember.js

Question

Answered
I've solved the problem, it has to do with my adapter, and I'll post more in an answer,
but here's a link to a problem I'm having with the fix Ember get not getting certain attribute
Original Question
I have the following code:
customerSignUp: function () {
var customer = this.get('store').createRecord('customer', {
description: 'Why hello sir'
});
var model = this.get('model');
model.set('customer', customer);
customer.save().then(function() {
model.save().then(function() {
customer.set('user', model);
customer.save();
});
});
}
With the following backing models:
App.User = App.Person.extend({
name: DS.attr('string'), // Actually their primary email.
customer: DS.belongsTo('customer', {async: true })
});
App.Customer = DS.Model.extend({
user: DS.belongsTo('user', {async: true}),
description: DS.attr('string')
});
(App.Person just passes along some naming conventions)
The customerSignUp function is trying to get both objects to refer to the other, so that either one could get attributes from the other as needed (the user model is planned to have more relationships like this in the future, so that one user can have multiple "roles" on the site).
The problem is that I can't get both to stably refer to each other. With this current implementation the model (user) points to the customer just fine, but the customer for some reason simply has it's user field set to <computed> in the Ember Debugger, and the record saved in the database doesn't even have a user field. It seems to me like some of my saves are overwriting the values or changing the underlying objects so they're no longer true? Honestly I'm just confused.
I've tried all kinds of different orderings of the saves and sets, but so far only one at a time works, or if both work, it's because I haven't saved one of them to the database. Any advice? Is this even necessary? Will the customer object have access to it's user even if there isn't an id explicitly stored in the customer?
Could this have to do with the adapter I'm using?
Update
With this implementation of customerSignUp:
customerSignUp: function () {
var model = this.get('model');
var customer = this.get('store').createRecord('customer', {
description: 'Why hello sir',
user: model
});
customer.save().then(function() {
model.set('customer', customer);
model.save();
});
}
The customer relationship on the user is set for a moment, but then resets to null. The user relationship is just <computed> and I don't think was ever set.

Answer 1

It had to do with my adapter.
This function:
serializeBelongsTo: function(record, json, relationship) {
console.log("serializeBelongsTo");
var attribute, belongsTo, key;
attribute = relationship.options.attribute || "id";
console.log(attribute);
key = relationship.key;
console.log(key);
belongsTo = Ember.get(record, key);
console.log(belongsTo);
if (Ember.isNone(belongsTo)) {
return;
}
var content = belongsTo.content;
console.log(content);
var temp = Ember.get(belongsTo, attribute);
console.log(temp);
json[key] = temp;
console.log(json);
if (relationship.options.polymorphic) {
return json[key + "_type"] = belongsTo.constructor.typeKey;
}
else {
return json;
}
returns a value of undefined from Ember.get(belongsTo, attribute) even though belongsTo and attribute are correctly set, although belongsTo has it's data buried in a content object, which this SO post details.