Reflections for REST API

I'm trying to build a (as close as it gets) generic REST API to simplyfy all the standard CRUD rest calls. For example I'd like to write one read method

models.{Entity}.findById(id)
  .exec(function(err, entity) {
    res(err, entity)
  }

{Entity} should be dynamically filled with a param from the rest call e.g.:

GET /api/v1/entity/:id/:type
GET /api/v1/entity/1234567890/user

Obviously I could do a semi-generic solution like this:

if (type === 'user') var query = models.User;

But that not really a nice solution in my opinion.

Questions

Is there an easy way to implement this and would this be viable on a bigger application? Cause everything I know about reflections from other languages their performance isn't that great.

Has anyone other recommendations on how I could implement such a framework?