Create snapshots on save not on flush

alows us to have access to changed attributes in snapshot

packages/ember-data/lib/system/model/model.js

@@ -889,7 +889,7 @@ var Model = Ember.Object.extend(Ember.Evented, {
   changedAttributes: function() {
     var oldData = get(this, '_data');
     var newData = get(this, '_attributes');
-    var diffData = {};
+    var diffData = Ember.create(null);
     var prop;
 
     for (prop in newData) {
@@ -899,11 +899,17 @@ var Model = Ember.Object.extend(Ember.Evented, {
     return diffData;
   },
 
+  flushChangedAttributes: function() {
+    this._inFlightAttributes = this._attributes;
+    this._attributes = Ember.create(null);
+  },
+
   /**
     @method adapterWillCommit
     @private
   */
   adapterWillCommit: function() {
+    this.flushChangedAttributes();
     this.send('willCommit');
   },
 
@@ -1052,8 +1058,6 @@ var Model = Ember.Object.extend(Ember.Evented, {
     var resolver = Ember.RSVP.defer(promiseLabel);
 
     this.store.scheduleSave(this, resolver);
-    this._inFlightAttributes = this._attributes;
-    this._attributes = Ember.create(null);
 
     return PromiseObject.create({
       promise: resolver.promise

packages/ember-data/lib/system/snapshot.js

@@ -27,6 +27,8 @@ function Snapshot(record) {
   this.type = record.constructor;
   this.modelName = record.constructor.modelName;
 
+  this._changedAttributes = record.changedAttributes();
+
   // The following code is here to keep backwards compatibility when accessing
   // `constructor` directly.
   //
@@ -135,7 +137,7 @@ Snapshot.prototype = {
     Example
 
     ```javascript
-    // store.push('post', { id: 1, author: 'Tomster', title: 'Hello World' });
+    // store.push('post', { id: 1, author: 'Tomster', title: 'Ember.js rocks' });
     postSnapshot.attributes(); // => { author: 'Tomster', title: 'Ember.js rocks' }
     ```
 
@@ -146,6 +148,31 @@ Snapshot.prototype = {
     return Ember.copy(this._attributes);
   },
 
+  /**
+    Returns all changed attributes and their old and new values.
+
+    Example
+
+    ```javascript
+    // store.push('post', { id: 1, author: 'Tomster', title: 'Ember.js rocks' });
+    postModel.set('title', 'Ember.js rocks!');
+    postSnapshot.changedAttributes(); // => { title: ['Ember.js rocks', 'Ember.js rocks!'] }
+    ```
+
+    @method changedAttributes
+    @return {Object} All changed attributes of the current snapshot
+  */
+  changedAttributes: function() {
+    var prop;
+    var changedAttributes = Ember.create(null);
+
+    for (prop in this._changedAttributes) {
+      changedAttributes[prop] = Ember.copy(this._changedAttributes[prop]);
+    }
+
+    return changedAttributes;
+  },
+
   /**
     Returns the current value of a belongsTo relationship.
 

packages/ember-data/lib/system/store.js

@@ -1254,8 +1254,9 @@ Store = Service.extend({
     @param {Resolver} resolver
   */
   scheduleSave: function(record, resolver) {
+    var snapshot = record._createSnapshot();
     record.adapterWillCommit();
-    this._pendingSave.push([record, resolver]);
+    this._pendingSave.push([snapshot, resolver]);
     once(this, 'flushPendingSave');
   },
 
@@ -1271,8 +1272,9 @@ Store = Service.extend({
     this._pendingSave = [];
 
     forEach(pending, function(tuple) {
-      var record = tuple[0];
+      var snapshot = tuple[0];
       var resolver = tuple[1];
+      var record = snapshot.record;
       var adapter = this.adapterFor(record.constructor);
       var operation;
 
@@ -1286,7 +1288,7 @@ Store = Service.extend({
         operation = 'updateRecord';
       }
 
-      resolver.resolve(_commit(adapter, this, operation, record));
+      resolver.resolve(_commit(adapter, this, operation, snapshot));
     }, this);
   },
 
@@ -2022,9 +2024,9 @@ function defaultSerializer(container) {
          container.lookup('serializer:-default');
 }
 
-function _commit(adapter, store, operation, record) {
-  var type = record.constructor;
-  var snapshot = record._createSnapshot();
+function _commit(adapter, store, operation, snapshot) {
+  var record = snapshot.record;
+  var type = snapshot.type;
   var promise = adapter[operation](store, type, snapshot);
   var serializer = serializerForAdapter(store, adapter, type);
   var label = "DS: Extract and notify about " + operation + " completion of " + record;
@@ -2040,15 +2042,15 @@ function _commit(adapter, store, operation, record) {
 
     store._adapterRun(function() {
       if (adapterPayload) {
-        payload = serializer.extract(store, type, adapterPayload, get(record, 'id'), operation);
+        payload = serializer.extract(store, type, adapterPayload, get(snapshot, 'id'), operation);
       }
       store.didSaveRecord(record, payload);
     });
 
     return record;
   }, function(reason) {
     if (reason instanceof InvalidError) {
-      var errors = serializer.extractErrors(store, type, reason.errors, get(record, 'id'));
+      var errors = serializer.extractErrors(store, type, reason.errors, get(snapshot, 'id'));
       store.recordWasInvalid(record, errors);
       reason = new InvalidError(errors);
     } else {

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

@@ -112,6 +112,20 @@ test("snapshot.attributes() returns a copy of all attributes for the current sna
   });
 });
 
+test("snapshot.changedAttributes() returns a copy of all changed attributes for the current snapshot", function() {
+  expect(1);
+
+  run(function() {
+    var post = env.store.push('post', { id: 1, title: 'Hello World' });
+    post.set('title', 'Hello World!');
+    var snapshot = post._createSnapshot();
+
+    var changes = snapshot.changedAttributes();
+
+    deepEqual(changes, { title: ['Hello World', 'Hello World!'] }, 'changed attributes are returned correctly');
+  });
+});
+
 test("snapshot.belongsTo() returns undefined if relationship is undefined", function() {
   expect(1);