[BUGFIX] Fix #7015 - calling changedAttributes for non instantiated relationships

Author: Igor Terzic

packages/-ember-data/tests/integration/snapshot-test.js

@@ -373,6 +373,42 @@ module('integration/snapshot - Snapshot', function(hooks) {
     assert.equal(relationship.attr('title'), 'Hello World', 'post title is correct');
   });
 
+  test('snapshot.belongsTo().changedAttributes() returns an empty object if belongsTo record in not instantiated #7015', function(assert) {
+    assert.expect(2);
+
+    store.push({
+      data: [
+        {
+          type: 'comment',
+          id: '2',
+          attributes: {
+            body: 'This is comment',
+          },
+          relationships: {
+            post: {
+              data: { type: 'post', id: '1' },
+            },
+          },
+        },
+      ],
+      included: [
+        {
+          type: 'post',
+          id: '1',
+          attributes: {
+            title: 'Hello World',
+          },
+        },
+      ],
+    });
+    let comment = store.peekRecord('comment', 2);
+    let snapshot = comment._createSnapshot();
+    let relationship = snapshot.belongsTo('post');
+
+    assert.ok(relationship instanceof Snapshot, 'snapshot is an instance of Snapshot');
+    assert.deepEqual(relationship.changedAttributes(), {}, 'changedAttributes are correct');
+  });
+
   test('snapshot.belongsTo() returns null if relationship is deleted', function(assert) {
     assert.expect(1);
 

packages/store/addon/-private/system/snapshot.ts

@@ -119,7 +119,6 @@ export default class Snapshot implements Snapshot {
      @type {String}
      */
     this.modelName = internalModel.modelName;
-
     if (internalModel.hasRecord) {
       this._changedAttributes = recordDataFor(internalModel).changedAttributes();
     }
@@ -246,6 +245,10 @@ export default class Snapshot implements Snapshot {
    */
   changedAttributes(): ChangedAttributesHash {
     let changedAttributes = Object.create(null);
+    if (!this._changedAttributes) {
+      return changedAttributes;
+    }
+
     let changedAttributeKeys = Object.keys(this._changedAttributes);
 
     for (let i = 0, length = changedAttributeKeys.length; i < length; i++) {