title: I cant seem to reference 2 schemas to populate after
body: <p>Theser are my two schemas that i want to ref.
  I want the listingsScheme userId to refer to the _id of userScheme. Its been 2 days working on this please help.</p>
  
  <pre><code>var userScheme = new Schema({
  email: { type: String },
  password: { type: String },
  fullName: { type: String },
  coverPhoto: { type: String},
  profilePhoto: { type: String},
  fbUserID: { type: String},
  profileExtraInfo: { type: Array},
  listings: {type: Schema.Types.ObjectId, ref: "Listings"}
  
  var listingsScheme = new Schema({
  category: { type: String, index: true }, 
  title: { type: String },
  description: { type: String },
  attributes: { type: Array },
  nrViews: {type: Number },
  photos: { type: Array },
  location: { type: Array, index: '2d' },
  created: { type: Date, index: true },
  updated: { type: Date },
  active: { type: Boolean, index: true } ,
  userId : { type: Schema.Types.ObjectId, ref : 'User' } ,
  fullName : { type: String },
  profilePhoto : { type : String},
  followers : {type : String},
  </code></pre>