Question

I’ll be as brief as possible.

I want to able to do this

{{ video.youtube_url.video_id }}

by implementing something like the following custom field:

class YouTubeURLField(URLField):
    description = _("YouTubeURL")

    def _video_id(self):
      return re.search('(?<=\?v\=)[\w-]+', self.value)
    video_id = property(_video_id)

    def __init__(self, verbose_name=None, name=None, verify_exists=True, **kwargs):
      super(YouTubeURLField, self).__init__(**kwargs)
      kwargs['max_length'] = kwargs.get('max_length', 200)
      CharField.__init__(self, verbose_name, name, **kwargs)
      self.validators.append(YouTubeURLValidator(verify_exists=verify_exists))

This:

    def _video_id(self):
      return re.search('(?<=\?v\=)[\w-]+', self.value)
    video_id = property(_video_id)

Does not sucessfully add a “video_id” attribute to my custom YouTubeURLField.

Everything else works flawlessly.

I understand there maybe better design considerations in terms of the YouTube custom field, but I’d rather just understand, first, why this doesn’t work.

Answer 1

I wanted to do it this way, because it seems it makes more sense from a design stand point. The video id is an attribute of the YouTube URL and not of the model itself.

I figured it out. I overrode the to_python function to return a YouTubeURL object.

class YouTubeURL(object):
  def __init__(self, value):
    self.value = value

  @property
  def video_id(self):
    regex = re.compile(r'/v/([A-Za-z0-9\-_]+)', re.IGNORECASE)

    id = regex.search(self.value)
    return id.group(1)

  def __unicode__(self):
    return "%s" % (self.value,)

  def __str__(self):
    return "%s" % (self.value,)

  def __len__(self):
    return len(self.value)

class YouTubeURLField(URLField):
    description = _("YouTubeURL")

    __metaclass__ = SubfieldBase

    def to_python(self, value):
      return YouTubeURL(value)

    def __init__(self, verbose_name=None, name=None, verify_exists=True, **kwargs):
      super(YouTubeURLField, self).__init__(**kwargs)
      kwargs['max_length'] = kwargs.get('max_length', 200)
      CharField.__init__(self, verbose_name, name, **kwargs)
      self.validators.append(YouTubeURLValidator(verify_exists=verify_exists))