ignore empty strings when setting ObjectIds

ignoreEmptyStrings.js

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

console.log('\n===========');
console.log('    mongoose version: %s', mongoose.version);
console.log('========\n\n');

var uri = 'mongodb://localhost/testing_optionalObjectid';
mongoose.connect(uri);
mongoose.connection.on('error', function () {
  console.error('connection error', arguments);
});

//
// ignore empty strings
//

function ignoreEmpty (val) {
  if ("" === val) {
    return undefined;
  } else {
    return val
  }
}

var schema = new Schema({
    name: String
  , oid : { type: Schema.ObjectId, set: ignoreEmpty }
});

var A = mongoose.model('A', schema);
var a = new A({ name: 'optionalObjectid', oid: '' });

a.save(function (err, a) {
  if (err) return done(err);

  A.findById(a, function (err, doc) {
    console.error('found', doc);
    done(err);
  });
})

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