Promise and nodejs MongoDB driver

Question

I would like to make a promise with the MongoDB driver. I wrote the following code: ``` var TaskBroker = function () { this.queueName = 'task_queue'; this.rabbit = {}; this.mongo = {}; }; TaskBroker.prototype.connectRabbit = function() { var self = this; return amqp.connect('amqp://localhost') .then(function(connection) { self.rabbit.connection = connection; return connection.createChannel() }) .then(function(channel) { self.rabbit.channel = channel; return channel.assertQueue(self.queueName, {durable: true}); }) }; TaskBroker.prototype.connectMongo = function() { console.log('Connect Mongo'); var self = this; var defer = q.defer(); MongoClient.connect('mongodb://127.0.0.1:27017/test', {}, defer.makeNodeResolver()); return defer.promise.then(function(db) { self.mongo.db = db; console.log('hello'); return 42; }); }; TaskBroker.prototype.connect = function () { var self = this; return this.connectRabbit() .then(self.connectMongo); }; ``` Do you have any idea why I don't have the output…

Accepted Answer

Manually promisifying an API is dangerous, I suggest something along the lines of:

```
TaskBroker.prototype._connectMongo = Q.nfcall(MongoClient.connect,
                                             'mongodb://127.0.0.1:27017/test',
                                            {});
TaskBroker.prototype.connectMongo = function(){
   return this._connectMongo().then(function(db){
       console.log("Hello");
       // self.stuff...
       return 42;
   }).catch(function(e){
       console.err("connection error",e); // log the connection error, or handler err
       throw e; // don't mark as handled, propagate the error.
   });
};
```

With Bluebird promises, that'd look something like:

```
var MongoClient = Promise.promisifyAll(require("mongodb").MongoClient);

TaskBroker.prototype.connectMongo = function(){
    return MongoClient.connectAsync().then(... 
        // Bluebird will automatically track unhandled errors        
};
```

Promise and nodejs MongoDB driver

Solution

Problem