Fix handling of relationship loading to use dataKey.

Data for a relationship should be looked up on the dataKey, and not the
plain property key. Previously, loads on a model with relationships
would not update the embedded models when the property key didn't
match the data key.

packages/ember-model/lib/model.js

@@ -128,7 +128,7 @@ Ember.Model = Ember.Object.extend(Ember.Evented, {
     this._reloadHasManys();
 
     // eagerly load embedded data
-    var relationships = this.constructor._relationships || [], meta = Ember.meta(this), relationshipKey, relationship, relationshipMeta, relationshipData, relationshipType;
+    var relationships = this.constructor._relationships || [], meta = Ember.meta(this), relationshipKey, relationship, relationshipMeta, dataKey, relationshipData, relationshipType;
     for (var i = 0, l = relationships.length; i < l; i++) {
       relationshipKey = relationships[i];
       relationship = (meta.descs || this)[relationshipKey];
@@ -140,7 +140,8 @@ Ember.Model = Ember.Object.extend(Ember.Evented, {
           relationshipType = Ember.get(Ember.lookup, relationshipType) || this.container.lookupFactory('model:'+ relationshipType);
         }
 
-        relationshipData = data[relationshipKey];
+        dataKey = this.dataKey(relationshipKey)
+        relationshipData = data[dataKey];
         if (relationshipData) {
           relationshipType.load(relationshipData);
         }

packages/ember-model/tests/has_many/embedded_objects_load_test.js

@@ -115,3 +115,44 @@ test("loading embedded data into a parent with deleted children deletes the chil
   equal(post.get('comments.length'), 1);
   equal(post.get('comments.firstObject.body'), 'new');
 });
+
+test("loading embedded data into a parent updates the child records with key option", function() {
+  expect(2);
+
+  var json = {
+    id: 1,
+    replies: [
+      {id: 1, body: 'new'}
+    ]
+  };
+
+  var Comment = Ember.Model.extend({
+    id: attr(),
+    body: attr()
+  });
+
+  Comment.adapter = {
+    find: function(record, id) {
+      record.load(id, {body: 'old'});
+    }
+  };
+
+  var Post = Ember.Model.extend({
+    id: attr(),
+    comments: Ember.hasMany(Comment, {key: 'replies', embedded: true})
+  });
+
+  Post.adapter = {
+    find: function(record, id) {
+      record.load(id, {replies: []});
+    }
+  };
+
+  var comment = Comment.find(1);
+  equal(comment.get('body'), 'old');
+
+  var post = Post.find(1);
+  post.load(1, json);
+
+  equal(comment.get('body'), 'new');
+});