Embedded Objects Mixin Works with the RESTSerializer

embedded_records_mixin.js

var get = Ember.get;
var forEach = Ember.EnumerableUtils.forEach;

/**
  The EmbeddedRecordsMixin allows you to add embedded record support to your
  serializers.
  To set up embedded records, you include the mixin into the serializer and then
  define your embedded relations.

  ```js
  App.PostSerializer = DS.RestSerializer.extend(DS.EmbeddedRecordsMixin, {
    attrs: {
      comments: {embedded: 'always'}
    }
  })
  ```

  Currently only `{embedded: 'always'}` records are supported.

  @class EmbeddedRecordsMixin
  @namespace DS
*/
DS.EmbeddedRecordsMixin = Ember.Mixin.create({
  pluralize: true,

  // added missing fields from the active model serializer
  keyForAttribute: function(attr) {
    return Ember.String.decamelize(attr);
  },

  keyForRelationship: function(key, kind) {
    key = Ember.String.decamelize(key);
    if (kind === "belongsTo") {
      return key + "_id";
    } else if (kind === "hasMany") {
      return Ember.String.singularize(key) + "_ids";
    } else {
      return key;
    }
  },

  /**
    Serialize has-may relationship when it is configured as embedded objects.

    @method serializeHasMany
  */
  serializeHasMany: function(record, json, relationship) {
    var key   = relationship.key,
        attrs = get(this, 'attrs'),
        embed = attrs && attrs[key] && attrs[key].embedded === 'always';

    if (embed) {
      json[this.keyForAttribute(key)] = get(record, key).map(function(relation) {
        var data = relation.serialize(),
            primaryKey = get(this, 'primaryKey');

        data[primaryKey] = get(relation, primaryKey);

        return data;
      }, this);
    }
  },

  /**
    Extract embedded objects out of the payload for a single object
    and add them as sideloaded objects instead.

    @method extractSingle
  */
  extractSingle: function(store, primaryType, payload, recordId, requestType) {
    var root = this.keyForAttribute(primaryType.typeKey),
        partial = payload[root];

    updatePayloadWithEmbedded(store, this, primaryType, partial, payload);

    return this._super(store, primaryType, payload, recordId, requestType);
  },

  /**
    Extract embedded objects out of a standard payload
    and add them as sideloaded objects instead.

    @method extractArray
  */
  extractArray: function(store, type, payload) {
    var root = this.keyForAttribute(type.typeKey),
        partials = payload[this.pluralize ? Ember.String.pluralize(root) : root];

    forEach(partials, function(partial) {
      updatePayloadWithEmbedded(store, this, type, partial, payload);
    }, this);
    
    return this._super(store, type, payload);
  }
});

function updatePayloadWithEmbedded(store, serializer, type, partial, payload) {
  var attrs = get(serializer, 'attrs');

  if (!attrs) {
    return;
  }

  type.eachRelationship(function(key, relationship) {
    var expandedKey, embeddedTypeKey, attribute, ids,
        config = attrs[key],
        serializer = store.serializerFor(relationship.type.typeKey),
        primaryKey = get(serializer, "primaryKey");

    if (relationship.kind !== "hasMany") {
      return;
    }

    if (config && (config.embedded === 'always' || config.embedded === 'load')) {
      // underscore forces the embedded records to be side loaded.
      // it is needed when main type === relationship.type
      embeddedTypeKey = '_' + Ember.String.pluralize(relationship.type.typeKey);
      expandedKey = this.keyForRelationship(key, relationship.kind);
      attribute  = this.keyForAttribute(key);
      ids = [];

      if (!partial[attribute]) {
        return;
      }

      payload[embeddedTypeKey] = payload[embeddedTypeKey] || [];

      forEach(partial[attribute], function(data) {
        var embeddedType = store.modelFor(relationship.type.typeKey);
        updatePayloadWithEmbedded(store, serializer, embeddedType, data, payload);
        ids.push(data[primaryKey]);
        payload[embeddedTypeKey].push(data);
      });

      partial[expandedKey] = ids;
      delete partial[attribute];
    }
  }, serializer);
}