invalidSet.js

var mongoose = require('mongoose');
var Schema = mongoose.Schema;
var assert = require('assert')

mongoose.connect('localhost', dbname);
mongoose.connection.on('error', function () {
  console.error('connection error', arguments);
});


var schema = new Schema({
    name: String
});

// custom validation during set
schema.path('name').set(function (v) {
  if (Array.isArray(v)) {
    this.invalidate('name', 'Cannot be an array', '['+v+']');
    return this.name;
  }
  return v;
})

var A = mongoose.model('A', schema);

mongoose.connection.on('open', function () {
  var a = new A({ name: ['setorder'] });
  a.save(done) // Validator "Cannot be an array" failed for path name with value `[setorder]`
});

function done (err) {
  if (err) console.error(err.stack);
  mongoose.connection.db.dropDatabase(function () {
    mongoose.connection.close();
  });
}