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

schema.path('name').set(function (v) {
  v = ('string' == typeof v && v || '').trim();

  // manual invalidation
  if (6 >= v.length)
    return this.invalidate('name', 'invalid length');

  return hash(v);
});

function hash (v) {
  return 'hashed ' + v
}

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

a = new A({ name: 'woot' });
a.validate(function (err) {
  console.log(err); // .. 'Validator "invalid length" failed for path name
  console.log(a);

  a = new A;
  a.name = 'long enough'
  a.validate(function (err) {
    console.log(err); // undefined
    console.log(a);
  });
});

If you add a 'required' SchemaType to the name path, then if the validation fails, it does so because the 'required' validator is not satisfied, but not because of the 'invalid length' validator.

I'm seeing the same as @systemovich. this.invalidate is being taken over by required error message.

@systemovich @andrejmead
so anyway to solve the required conflict?