Mongoose promise uncaught exception

[perrin4869]

I finally got around to promisifying the application I'm working on, and I stumbled upon the following bug when saving a duplicate record with a callback instead of a promise. I added sample code below reproducing the error: when attempting a duplicate insert with a promise and a catch, nothing special happens, but when doing it with a callback it outputs an uncaught exception.

var mongoose = require('mongoose'),
        Promise  = require('bluebird');
mongoose.Promise = Promise;

UserSchema = new mongoose.Schema({
        _id: String
});
User = mongoose.model('User', UserSchema);

mongoose.connect('mongodb://localhost/mongoose_promise', function() {
        var user = new User({ _id: 'a' });
        user.save().then(function(res) {
                var user2 = new User({ _id: 'a' });
                user2.save().catch(function(err) {
                        console.log("Caught error - Promise");
                });

                var user3 = new User({ _id: 'a' });
                user3.save(function(err) {
                        if(err) console.log("Caught error - Callback");
                });
        });
});

Output:

Caught error - Promise
Caught error - Callback
Unhandled rejection MongoError: E11000 duplicate key error index: mongoose_promise.users.$_id_ dup key: { : "a" }
    at Function.MongoError.create (/home/perrin4869/projects/nodejs/mongoose_promise/node_modules/mongoose/node_modules/mongodb/node_modules/mongodb-core/lib/error.js:31:11)
    at toError (/home/perrin4869/projects/nodejs/mongoose_promise/node_modules/mongoose/node_modules/mongodb/lib/utils.js:113:22)
    at /home/perrin4869/projects/nodejs/mongoose_promise/node_modules/mongoose/node_modules/mongodb/lib/collection.js:547:23
    at /home/perrin4869/projects/nodejs/mongoose_promise/node_modules/mongoose/node_modules/mongodb/lib/bulk/unordered.js:457:9
    at resultHandler (/home/perrin4869/projects/nodejs/mongoose_promise/node_modules/mongoose/node_modules/mongodb/lib/bulk/unordered.js:409:5)
    at /home/perrin4869/projects/nodejs/mongoose_promise/node_modules/mongoose/node_modules/mongodb/node_modules/mongodb-core/lib/topologies/server.js:756:13
    at Callbacks.emit (/home/perrin4869/projects/nodejs/mongoose_promise/node_modules/mongoose/node_modules/mongodb/node_modules/mongodb-core/lib/topologies/server.js:95:3)
    at null.messageHandler (/home/perrin4869/projects/nodejs/mongoose_promise/node_modules/mongoose/node_modules/mongodb/node_modules/mongodb-core/lib/topologies/server.js:243:23)
    at Socket.<anonymous> (/home/perrin4869/projects/nodejs/mongoose_promise/node_modules/mongoose/node_modules/mongodb/node_modules/mongodb-core/lib/connection/connection.js:262:22)
    at Socket.emit (events.js:107:17)
    at readableAddChunk (_stream_readable.js:163:16)
    at Socket.Readable.push (_stream_readable.js:126:10)
    at TCP.onread (net.js:538:20)

If you remove the line mongoose.Promise = Promise; then the callback stops outputting the message.

[vkarpov15]

For backwards compat until #2917, mongoose returns mpromise promises, which do not have a .catch(). Feel free to nag for that at aheckmann/mpromise#14, however, its not a priority going forward since mongoose will no longer support mpromise in its next major release. I would strongly recommend you set mongoose's promise lib with mongoose.Promise = global.Promise; or similar if you want to use mongoose with promises.

The reason why you're not getting any messages if you don't use an ES6-compatible promises lib like Bluebird is that the user2.save().catch() call crashes out and rejects the promise. For instance, if you run the below script:

var mongoose = require('mongoose'),
        Promise  = require('bluebird');
//mongoose.Promise = Promise;

mongoose.set('debug', true);

UserSchema = new mongoose.Schema({
        _id: String
});
User = mongoose.model('User', UserSchema);

mongoose.connect('mongodb://localhost/gh3355', function() {
  User.remove(function() {
    next();
  });
});

function next() {
        var user = new User({ _id: 'a' });
        user.save().then(function(res) {
                var user2 = new User({ _id: 'a' });
                user2.save().catch(function(err) {
                        console.log("Caught error - Promise");
                });
                console.log(1);

                var user3 = new User({ _id: 'a' });
                user3.save(function(err) {
                        if(err) console.log("Caught error - Callback");
                });
        }).then(null, function(error) { console.log(error.stack); });
}

You should see the error:

TypeError: undefined is not a function
    at /home/val/Workspace/10gen/troubleshoot-mongoose/gh-3355.js:22:35
    at newTickHandler (/home/val/Workspace/10gen/mongoose/node_modules/mpromise/lib/promise.js:229:18)
    at process._tickCallback (node.js:355:11)

[kog13]

@vkarpov15 mongoose.Promise = global.Promise was exactly what I was looking for. Thank you so much for the recommendation.