Mongoose pre.save() async middleware not working as expected

Question

Following up from : Mongoose unique validation error type

I'm using this schema with mongoose 3.0.3 from npm:

var schema = new Schema({      _id: Schema.ObjectId,     email: {type: String, required: true, unique: true}  }); 

With this middleware to get a validationError from unique:true

schema.pre("save", function(next, done) {     var self = this;      model.findOne({email : this.email}, 'email', function(err, results) {         if(err) {             done(err);         } else if(results) {             console.warn('results', results);             self.invalidate("email", "email must be unique");             done(new Error("email must be unique"));         } else {             done();         }     });      next(); }); 

However, it does not work!

Users.create() will still return a a MongoError: E11000 duplicate key error index and the console.warn() is only called after that.

The save action should not be called until all middleware done()have been called according to the docs, and I should get back a validation error.

It looks like the done() behavior is not working as expected,

Any idea why?

Answer 1

You're using a parallel middleware callback function (with both next and done), but you're not setting the parallel flag in the schema.pre parameters so it's using the serial rules.

So either include the parallel flag in your call:

schema.pre("save", true, function(next, done) { ... 

Or switch to a serial middleware callback style if that's all you need anyway:

schema.pre("save", function(next) {     var self = this;      model.findOne({email : this.email}, 'email', function(err, results) {         if(err) {             next(err);         } else if(results) {             console.warn('results', results);             self.invalidate("email", "email must be unique");             next(new Error("email must be unique"));         } else {             next();         }     }); });