<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def key(self):
 """ A property to return the key used in redis for the current field. """

        return self.make_key(
            self._instance._name,
            self._instance.pk.get(),
            self.name,
        )