title: Mongoose schema reference
body: <p>Is it possible to have a Schema to reference another Schema within Mongo?</p>
  
  <p>I've got the below, where i would like the user in the Line schema to be a user from the UserSchema</p>
  
  <pre><code>var UserSchema = new Schema({
      name: {type: String, required: true},
      screen_name: {type: String, required: true, index:{unique:true}},
      email: {type: String, required: true, unique:true},
      created_at: {type: Date, required: true, default: Date}
  });
  
  
  var LineSchema = new Schema({
      user: [UserSchema],
      text: String,
      entered_at: {type: Date, required: true, default: Date}
  });
  
  
  var StorySchema = new Schema ({
      sid: {type: String, unique: true, required: true},
      maxlines: {type: Number, default: 10}, // Max number of lines per user
      title: {type: String, default: 'Select here to set a title'},
      lines: [LineSchema],
      created_at: {type: Date, required: true, default: Date}
  });
  
  
  var Story = db.model('Story', StorySchema);
  var User = db.model('User', UserSchema);
  </code></pre>