new_contents: """This module defines the format used by marshall to map the models."""
  from flask_restful import fields
  
  bucketlistitem_serializer = {
      'id': fields.Integer,
      'item_name': fields.String,
      'priority': fields.String,
      'done': fields.Boolean,
      'date_created': fields.DateTime,
      'date_modified': fields.DateTime
  }
  
  bucketlist_serializer = {
      'id': fields.Integer,
      'list_name': fields.String,
      'bucketlist_items': fields.Nested(bucketlistitem_serializer),
      'created_by': fields.Integer
  }
  
  user_serializer = {
      'id': fields.Integer,
      'username': fields.String,
      'bucketlists': fields.Nested(bucketlist_serializer)
  }
  
subject: Add marshal fields to map with models.