old_contents: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from __future__ import unicode_literals
  
  from flask.ext.mongoengine import MongoEngine
  
  db = MongoEngine()
  
  
  class Disaster(db.Document):
      source = db.StringField(required=True)
      source_id = db.StringField(required=True)
      type = db.StringField()
      properties = db.DictField()
      geometry = db.DictField()
  
      meta = {"indexes": [{"fields": ["geometry.coordinates"]}]}
  
      def asdict(self):
          return {
              "id": "{}".format(self["id"]),
              "source": self["source"],
              "source_id": self["source_id"],
              "type": self["type"],
              "properties": self["properties"],
              "geometry": self["geometry"],
          }
  
new_contents: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from __future__ import unicode_literals
  
  from datetime import datetime
  from flask.ext.mongoengine import MongoEngine
  
  db = MongoEngine()
  
  
  class Disaster(db.Document):
      source = db.StringField(required=True)
      source_id = db.StringField(required=True)
      type = db.StringField()
      properties = db.DictField()
      geometry = db.DictField()
      modified_at = db.DateTimeField(default=datetime.utcnow)
  
      meta = {"indexes": [{"fields": ["geometry.coordinates"]}]}
  
      def asdict(self):
          return {
              "id": "{}".format(self["id"]),
              "source": self["source"],
              "source_id": self["source_id"],
              "type": self["type"],
              "properties": self["properties"],
              "geometry": self["geometry"],
          }
  
subject: add modified_at column