How about my own types?
The things it supports can be found in the tests https://github.com/bouk/gonerics/blob/master/template_params...
Although I'm not a believer in generic but I think it's a bfd in the programming field which will be as important as the REST thesis, or ror.
How about a service with similar approach that offers Parse to appengine migration: user calls a rest point like: generics.io/parse/github.com/crazychrome/package/user to configure fields and types requirements, then the service generate a repo contains codes can be deployed to appengine and 100% compatible with what Parse offers.