code: def _get_pk(self):
          
          pk = super(ExtendedCollectionManager, self)._get_pk()
  
          if pk is not None and isinstance(pk, RawFilter):
              # We have a RedisModel and we want its pk, or a RedisField
              # (single value) and we want its value
              if isinstance(pk.value, RedisModel):
                  pk = pk.value.pk.get()
              elif isinstance(pk.value, SingleValueField):
                  pk = pk.value.proxy_get()
              else:
                  raise ValueError(u'Invalide filter value for a PK: %s' % pk.value)
  
          return pk
docs: Override the default _get_pk method to retrieve the real pk value if we
          have a SingleValueField or a RedisModel instead of a real PK value