city.js

import mongoose from 'mongoose'

let CitySchema = new mongoose.Schema({
  name:     { type: String, required: true },
  country:  { type: String, required: true },
  province: { type: String, required: true },
  location: { type: [Number], required: true, index: '2d' }
})

CitySchema.pre('validate', next => {
  console.log(Date.now(), 'validate pre-hook', this)
  next()
})

export default mongoose.model('City', CitySchema)

database.js

import mongoose from 'mongoose'
import {mongodb} from '../config'
import logger from './logger'

var uri = `${mongodb.host}:${mongodb.port}/${mongodb.database}`

if(mongodb.username && mongodb.password) {
  uri = `${mongodb.username}:${mondob.password}@uri`
}

mongoose.connect('mongodb://' + uri)

var database = mongoose.connection
database.once('open', logger.info.bind(null, 'Database successfully connected'))
database.on('error', (e) => {
  logger.error('Could not establish connection to database', {
    uri: uri,
    error: e
  })
})

export default database

gistfile1.sh

> var db = require('./lib/support/database')
2015-04-16T01:32:50.789Z - info: Config loaded from development.js
undefined
> 2015-04-16T01:32:50.904Z - info: Database successfully connected
> var City = require('./lib/models/city')
undefined
> var c = new City({name: "Perth", country: "Australia", province: "Western Australia" })
undefined
> c.save()
1429148012090 'validate pre-hook' undefined
{ emitter:
   { domain: null,
     _events: { reject: [Function] },
     _maxListeners: 10 },
  emitted: {},
  ended: true }