From a2836fbb56cd10259a90ee125938e7cda4ab13c1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Miroslav=20Bajto=C5=A1?= <miroslav@strongloop.com>
Date: Tue, 17 Feb 2015 17:31:42 +0100
Subject: [PATCH] ModelBaseClass: support promise-based observers

Allow the observer functions passed to `ModelBaseClass.observe`
to return a promise instead of calling the callback.
---
 lib/model.js                | 10 +++++++++-
 package.json                |  1 +
 test/async-observer.test.js | 22 ++++++++++++++++++++++
 3 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/lib/model.js b/lib/model.js
index dadb722d..0a3ca8c0 100644
--- a/lib/model.js
+++ b/lib/model.js
@@ -567,7 +567,15 @@ ModelBaseClass.notifyObserversOf = function(operation, context, callback) {
 
     async.eachSeries(
       observers,
-      function(fn, next) { fn(context, next); },
+      function notifySingleObserver(fn, next) {
+        var retval = fn(context, next);
+        if (retval && typeof retval.then === 'function') {
+          retval.then(
+            function() { next(); },
+            next // error handler
+          );
+        }
+      },
       function(err) { callback(err, context) }
     );
   });
diff --git a/package.json b/package.json
index 6d0a6d03..e4a7091e 100644
--- a/package.json
+++ b/package.json
@@ -23,6 +23,7 @@
     "node >= 0.6"
   ],
   "devDependencies": {
+    "bluebird": "^2.9.9",
     "mocha": "^2.1.0",
     "should": "^5.0.0"
   },
diff --git a/test/async-observer.test.js b/test/async-observer.test.js
index 32040018..47b32324 100644
--- a/test/async-observer.test.js
+++ b/test/async-observer.test.js
@@ -1,5 +1,6 @@
 var ModelBuilder = require('../').ModelBuilder;
 var should = require('./init');
+var Promise = global.Promise || require('bluebird');
 
 describe('async observer', function() {
   var TestModel;
@@ -93,6 +94,27 @@ describe('async observer', function() {
       done();
     });
   });
+
+  it('resolves promises returned by observers', function(done) {
+    TestModel.observe('event', function(ctx) {
+      return Promise.resolve('value-to-ignore');
+    });
+    TestModel.notifyObserversOf('event', {}, function(err, ctx) {
+      // the test times out when the promises are not supported
+      done();
+    });
+  });
+
+  it('handles rejected promise returned by an observer', function(done) {
+    var testError = new Error('expected test error');
+    TestModel.observe('event', function(ctx) {
+      return Promise.reject(testError);
+    });
+    TestModel.notifyObserversOf('event', {}, function(err, ctx) {
+      err.should.eql(testError);
+      done();
+    });
+  });
 });
 
 function pushAndNext(array, value) {