ModelBaseClass: promise mode for notifyObserversOf

Support both promise and callback styles in
ModelBaseClass.notifyObserversOf.

When there is no callback supplied, the method returns a promise that
is resolved (or rejected) with the result.

lib/model.js

@@ -561,6 +561,8 @@ ModelBaseClass.observe = function(operation, listener) {
 ModelBaseClass.notifyObserversOf = function(operation, context, callback) {
   var observers = this._observers && this._observers[operation];
 
+  if (!callback) callback = utils.createPromiseCallback();
+
   this._notifyBaseObservers(operation, context, function doNotify(err) {
     if (err) return callback(err, context);
     if (!observers || !observers.length) return callback(null, context);
@@ -579,6 +581,7 @@ ModelBaseClass.notifyObserversOf = function(operation, context, callback) {
       function(err) { callback(err, context) }
     );
   });
+  return callback.promise;
 }
 
 ModelBaseClass._notifyBaseObservers = function(operation, context, callback) {

lib/utils.js

@@ -9,6 +9,7 @@ exports.defineCachedRelations = defineCachedRelations;
 exports.sortObjectsByIds = sortObjectsByIds;
 exports.setScopeValuesFromWhere = setScopeValuesFromWhere;
 exports.mergeQuery = mergeQuery;
+exports.createPromiseCallback = createPromiseCallback
 
 var traverse = require('traverse');
 
@@ -340,3 +341,30 @@ function sortObjectsByIds(idName, ids, objects, strict) {
   
   return heading.concat(tailing);
 };
+
+function createPromiseCallback() {
+  var cb;
+
+  if (!global.Promise) {
+    cb = function(){};
+    cb.promise = {};
+    Object.defineProperty(cb.promise, 'then', { get: throwPromiseNotDefined });
+    Object.defineProperty(cb.promise, 'catch', { get: throwPromiseNotDefined });
+    return cb;
+  }
+
+  var promise = new Promise(function (resolve, reject) {
+    cb = function (err, data) {
+      if (err) return reject(err);
+      return resolve(data);
+    };
+  });
+  cb.promise = promise;
+  return cb;
+}
+
+function throwPromiseNotDefined() {
+  throw new Error(
+    'Your Node runtime does support ES6 Promises. ' +
+    'Set "global.Promise" to your preferred implementation of promises.');
+}

test/async-observer.test.js

@@ -1,6 +1,5 @@
 var ModelBuilder = require('../').ModelBuilder;
 var should = require('./init');
-var Promise = global.Promise || require('bluebird');
 
 describe('async observer', function() {
   var TestModel;
@@ -115,6 +114,28 @@ describe('async observer', function() {
       done();
     });
   });
+
+  it('returns a promise when no callback is provided', function() {
+    var context = { value: 'a-test-context' };
+    var p = TestModel.notifyObserversOf('event', context);
+    (p !== undefined).should.be.true;
+    return p.then(function(result) {
+      result.should.eql(context);
+    });
+  });
+
+  it('returns a rejected promise when no callback is provided', function() {
+    var testError = new Error('expected test error');
+    TestModel.observe('event', function(ctx, next) { next(testError); });
+    var p = TestModel.notifyObserversOf('event', context);
+    return p.then(
+      function(result) {
+        throw new Error('The promise should have been rejected.');
+      },
+      function(err) {
+        err.should.eql(testError);
+      });
+  });
 });
 
 function pushAndNext(array, value) {

test/init.js

@@ -26,3 +26,7 @@ if (!('getModelBuilder' in global)) {
     return new ModelBuilder();
   };
 }
+
+if (!('Promise' in global)) {
+  global.Promise = require('bluebird');
+}