How to config nginx-memcached?

hi all:

 I would like to serve a application , there comes a request with an

arguement ,then nginx use this argument as the memcache_key . if hit
,return the value to client directly, if not hit, rewrite the request to
my backend server(python + django) and with the arguement

it likes:

first: http://myserver:7214/cache/?XXX

      hit:  return memcached value with key XXX

     not hit:  rewrite the request like :
         http://myserver:7214/gen/?XXX     and use proxy_pass to

I am working on it for serveral days and can’t work it out ,
thanks a lot