Don't return promise if callback specified

Hello, I’m the author of meanify, a library that uses Mongoose to cleverly generate API routes.

One of my users is bumping into an issue where he is seeing console.error output because I use callbacks to deal with Mongoose errors.

Bluebird appears to expect an explicit catch statement, forcing one to prefer one style to another i.e. promises vs callbacks upon installation.

Consider the following code:

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

var User = mongoose.model('User', new mongoose.Schema({
    name: { type: String, required: true },
}));

var user = new User();
user.save(function (err, doc) {
  if (err) {
    // error handled in the callback
    console.error('Error:', err.message);
  } else {
    console.log('Success:', doc);
  }
});

Results in this console output:

Error: User validation failed
Unhandled rejection ValidationError: User validation failed
    at MongooseError.ValidationError (/Users/artz/Sites/meanify/node_modules/mongoose/lib/error/validation.js:23:11)
    at model.Document.invalidate (/Users/artz/Sites/meanify/node_modules/mongoose/lib/document.js:1298:32)
    at /Users/artz/Sites/meanify/node_modules/mongoose/lib/document.js:1173:16
    at validate (/Users/artz/Sites/meanify/node_modules/mongoose/lib/schematype.js:662:7)
    at /Users/artz/Sites/meanify/node_modules/mongoose/lib/schematype.js:693:9
    at Array.forEach (native)
    at SchemaString.SchemaType.doValidate (/Users/artz/Sites/meanify/node_modules/mongoose/lib/schematype.js:667:19)
    at /Users/artz/Sites/meanify/node_modules/mongoose/lib/document.js:1171:9
    at nextTickCallbackWith0Args (node.js:452:9)
    at process._tickCallback (node.js:381:13)
    at Function.Module.runMain (module.js:449:11)
    at startup (node.js:139:18)
    at node.js:999:3

My only solution to avoid this error for my users using Bluebird appears to be refactoring meanify to use promises so there’s no error output. Any advice would be much appreciated.

Thanks!

[vkarpov15]

Right now mongoose always returns a promise, even if you specify a callback. I’d love to change this for a future release. However, not happening anytime soon because we’ve got more pressing issues. Here’s a couple alternatives:

1. Don’t use bluebird. IMO it’s a bloated mess that’s more trouble than it’s worth
2. Use .catch() with an empty function

user.save(function (err, doc) {
  if (err) {
    // error handled in the callback
    console.error('Error:', err.message);
  } else {
    console.log('Success:', doc);
  }
}).catch(function() {});

[vkarpov15]

Closing this in favor of #3670, follow that issue for updates. Still planning on changing this for 5.0.