def openlibrary_url(self): return id_url('olwk', self.openlibrary_id)
def librarything_url(self): return id_url('ltwk', self.librarything_id)
def googlebooks_url(self): return id_url('goog', self.googlebooks_id)
def goodreads_url(self): return id_url('gdrd', self.goodreads_id)
def url(self): return id_url(self.type, self.value)