code: def get_document_value(document, key):
      '''
      Returns the display value of a field for a particular MongoDB document.
      '''
      value = getattr(document, key)
      if isinstance(value, ObjectId):
          return value
  
      if isinstance(document._fields.get(key), URLField):
          return mark_safe(.format(value, value))
  
      if isinstance(value, Document):
          app_label = value.__module__.replace(".models", "")
          document_name = value._class_name
          url = reverse(
              "document_detail",
              kwargs={'app_label': app_label, 'document_name': document_name,
                      'id': value.id})
          return mark_safe("""<a href="{0}">{1}</a>""".format(url, value))
  
      return value
docs: Returns the display value of a field for a particular MongoDB document.