def gen_url_regex(resource):
    """ URL regex for resource class generator. """
    if resource._meta.parent:
        yield resource._meta.parent._meta.url_regex.rstrip('/$').lstrip('^')
    for p in resource._meta.url_params:
        yield '%(name)s/(?P<%(name)s>[^/]+)' % dict(name=p)
    if resource._meta.prefix:
        yield resource._meta.prefix
    yield '%(name)s/(?P<%(name)s>[^/]+)?' % dict(name=resource._meta.name)
