Serialize ids when saving emberjs model - node.js

Question

I have an emberjs application backed by a nodejs server and mongodb. Currently my database is sending documents with an '_id' field. I have the followign code to force Ember to treat '_id' as the primary key:
App.ApplicationSerializer = DS.RESTSerializer.extend({
primaryKey: '_id'
});
On the other hand i have two models related by a 'hasMany' relationship as such:
App.Player = DS.Model.extend({
name: DS.attr('string'),
thumbLink: DS.attr('string'),
activeGame: DS.belongsTo('game', { async: true }),
email: DS.attr('string'),
firstName: DS.attr('string'),
lastName: DS.attr('string'),
admin: DS.attr('boolean')
});
App.Game = DS.Model.extend({
name: DS.attr('string'),
active: DS.attr('boolean'),
players: DS.hasMany('player', { async: true })
});
The problem is that when i try to save the model ( this.get('model').save() )on my controller the ids are not serialized and the result is ember sending the following:
{"game":{"name":"Indie/Rock","active":false,"players":[],"_id":"53cbbf43daa978983ee0b101"}}
As you can see the players array is empty, and as a result, the server is saving that empty array which in fact is not correct. I am aware that it is possible to use { embedded: true } on the models and return the models with embedded documents from the server, but i want to preserve the async feature.
I have tried to extend the game serializer from EmbeddedRecordsMixing as the following:
App.GameSerializer = DS.ActiveModelSerializer
.extend(DS.EmbeddedRecordsMixin)
.extend({
attrs: {
players: {serialize: 'ids', deserialize: 'ids'},
}
});
But when i do so i get the following error from ember even though the ApplicationSerializer is suppossedly telling Ember to user _id as primary key:
Assertion Failed: Error: Assertion Failed: You must include an `id` for App.Game in a hash passed to `push`
My question is if it is possible to maintain the async features of ember-data while being able to serialize the document with the ids on it's relation and using _id as a primary key.
Thank you.

Answer 1

Ember Data is stupid in this aspect, if it's a ManyToOne relationship, it only includes the id from the belongsTo side. Honestly I've had it on my bucket list to submit a PR, but time is limited.
https://github.com/emberjs/data/commit/7f752ad15eb9b9454e3da3f4e0b8c487cdc70ff0#commitcomment-4923439
App.ApplicationSerializer = DS.RESTSerializer.extend({
serializeHasMany: function(record, json, relationship) {
var key = relationship.key;
var payloadKey = this.keyForRelationship ? this.keyForRelationship(key, "hasMany") : key;
var relationshipType = RelationshipChange.determineRelationshipType(record.constructor, relationship);
if (relationshipType === 'manyToNone' || relationshipType === 'manyToMany'
|| relationshipType === 'manyToOne') { // This is the change
json[payloadKey] = get(record, key).mapBy('id');
// TODO support for polymorphic manyToNone and manyToMany relationships
}
},
});