how to implement the function like left join of mysql in mongoose

I am going to implement the function like left join of mysql in mongoose. the date is

var mongoose = require('mongoose')
  , Schema = mongoose.Schema

var personSchema = Schema({
  _id     : Number,
  name    : String
});

var storySchema = Schema({
  _creator : { type: Number, ref: 'Person' },
  title    : String
});

var personProfile = Schema({
   userid : {type: Number, ref: 'Person'},
   birthday: Date,
   profilelink: String,
   email: String
});

var Story  = mongoose.model('Story', storySchema);
var Person = mongoose.model('Person', personSchema);
var personProfile = mongoose.model('Personprofile', personProfile );

I am going to display the Story model with the user profile. We have to get the profile info with the _creator of story and the userid of personProfile

How can I get the info using mongoose query?

Thanks Nelis