old_contents: """Django DDP utils for DDP messaging."""
  from dddp import THREAD_LOCAL as this
  
  
  def obj_change_as_msg(obj, msg):
      """Generate a DDP msg for obj with specified msg type."""
      serializer = this.serializer
      data = serializer.serialize([obj])[0]
  
      # collection name is <app>.<model>
      name = data['model']
  
      # cast ID as string
      if not isinstance(data['pk'], basestring):
          data['pk'] = '%d' % data['pk']
  
      payload = {
          'msg': msg,
          'collection': name,
          'id': data['pk'],
      }
      if msg != 'removed':
          payload['fields'] = data['fields']
  
      return (name, payload)
  
new_contents: """Django DDP utils for DDP messaging."""
  from copy import deepcopy
  from dddp import THREAD_LOCAL as this
  from django.db.models.expressions import ExpressionNode
  
  
  def obj_change_as_msg(obj, msg):
      """Generate a DDP msg for obj with specified msg type."""
      # check for F expressions
      exps = [
          name for name, val in vars(obj).items()
          if isinstance(val, ExpressionNode)
      ]
      if exps:
          # clone and update obj with values but only for the expression fields
          obj = deepcopy(obj)
          # Django 1.8 makes obj._meta public --> pylint: disable=W0212
          for name, val in obj._meta.model.objects.values(*exps).get(pk=obj.pk):
              setattr(obj, name, val)
  
      # run serialization now that all fields are "concrete" (not F expressions)
      serializer = this.serializer
      data = serializer.serialize([obj])[0]
  
      # collection name is <app>.<model>
      name = data['model']
  
      # cast ID as string
      if not isinstance(data['pk'], basestring):
          data['pk'] = '%d' % data['pk']
  
      payload = {
          'msg': msg,
          'collection': name,
          'id': data['pk'],
      }
      if msg != 'removed':
          payload['fields'] = data['fields']
  
      return (name, payload)
  
subject: Support serializing objects that are saved with F expressions by reading field values for F expressions from database explicitly before serializing.