Mongoose Unique Validation

mongoose-unique-validator.js

/**
 * Dependencies
 */
var MongooseError = require('mongoose/lib/error')
,   Promise       = require('bluebird');

/**
 * Module body / Expose
 */
var parseError = function (err, options) {
  options = options || {};

  if (err && err.name === 'MongoError' &&
    (err.code === 11000 || err.code === 11001)
  ) {
    var field = err.message.split('index: ')[1].split(' ')[0].split('_')[0]
    ,   value = err.message.split('"')[1]
    ,   error = new MongooseError.ValidationError(err);

    error.errors[field] = new MongooseError.ValidatorError({
      type: 'Duplicate Value',
      path: field,
      value: value,
      message: options.message || null
    });

    return error;
  } else {
    return err;
  }
};

module.exports = function (schema, options) {
  options = options || {};
  options.errors = options.errors || {};

  schema.methods.write = function () {
    var self = this;
    return new Promise(function (resolve, reject) {
      self.save(function (err) {
        err = parseError(err, options.errors.unique);
        if (err) return reject(err);
        resolve(self);
      });
    });
  };
};