596.js

var mongoose = require('./../mongoose');
mongoose.connect('localhost', 'testing_596');

function validatePresenceOf (value) {
  console.error('validating ', value);
  if (value === null) return false;
  return value;
};

var AccountSchema =  new mongoose.Schema({
    balance: {type: Number, validate: [validatePresenceOf, 'nooooooooooooooooo']}
});

var A = mongoose.model('Customer', new mongoose.Schema({
    name    : String
  , email : String
  , accounts: [AccountSchema]
}));

mongoose.connection.on('open', function () {
  var a = new A;
  a.accounts.push({ balance: 3.43});
  a.accounts.push({ balance: "" });
  a.accounts.push({ balance: "twenty" });

  a.save(function (err) {
    if (err) console.error(err.stack||err);
    console.error('isnew %s', a.isNew);
    mongoose.connection.db.dropDatabase(function () {
      mongoose.connection.close();
    });
  });
});