How to create Model Classes(NSObject) automatically from json dictionary?

is there any way to create model classes(wrapper) of dictionary or json responce? because in my app there are many webservices and all WS contains big data. if i am creating all the time one by one it takes much time to create NSObject Class with Checking Null data and Encode-Decode Object. either please suggest me it is right way to create all NSObject manually? i can't want to parse direct dictionary. Thanks.