Add $update method, fixes FirebaseExtended#238

angularfire.js

@@ -241,6 +241,27 @@
         return deferred.promise;
       };
 
+      // Non-destructively update only a subset of keys for the current object.
+      // This is the equivalent of calling `update()` on a Firebase reference.
+      // Takes a single mandatory argument:
+      //
+      //    * `newValue`: The set of keys and values that must be updated for
+      //                  this location.
+      //
+      // This function returns a promise that will be resolved when the data
+      // has been successfully saved to the server.
+      object.$update = function(newValue) {
+        var deferred = self._q.defer();
+        self._fRef.ref().update(self._parseObject(newValue), function(err) {
+          if (err) {
+            deferred.reject(err);
+          } else {
+            deferred.resolve();
+          }
+        });
+        return deferred.promise;
+      };
+
       // Update a value within a transaction. Calling this is the
       // equivalent of calling `transaction()` on a Firebase reference.
       //

tests/e2e/test_chat.js

@@ -88,6 +88,33 @@ casper.then(function() {
   });
 });
 
+casper.then(function() {
+  var _testName = "GuestTest";
+  var _testMessage = "Modified test message";
+
+  this.evaluate(function(params) {
+    window.__flag = false;
+    var idx = _scope.messages.$getIndex();
+    var key = idx[idx.length-1];
+    var obj = {}; obj[key] = {from: params[0], content: params[1]};
+    _scope.messages.$update(obj).then(function() {
+      window.__flag = true;
+    });
+  }, [_testName, _testMessage]);
+
+  this.waitFor(function() {
+    return this.getGlobal("__flag") === true;
+  }, function() {
+    this.test.assertEval(function(params) {
+      var msgs = document.querySelectorAll(".messageBlock");
+      if (msgs.length != 2) {
+        return false;
+      }
+      return testIfInDOM(params[0], params[1], msgs[1]);
+    }, "Testing if $update works", [_testName, _testMessage]);
+  });
+});
+
 casper.then(function() {
   this.test.assertEval(function() {
     _scope.message = "Limit Test";