SiftImportUser.swift

extension User {

    @NSManaged var lastName: String?
    @NSManaged var name: String?
    @NSManaged var userId: NSNumber?
    @NSManaged var createdEvents: NSSet?
    @NSManaged var homeCity: City?

}

extension User {
   override class var map:[String : String] {
      return [ "userId" : "id", 
               "lastName" : "last_name", 
               "homeCity" : "home_city", 
               "createdEvents" : "events"]
   }

   override class var relatedByAttribute: String {
      return "userId"
   }
   
   override class var relatedJsonKey: String {
      return "id"
   }
}

...

let data:NSData = ...
let context = ..
do {
 let user:User? = try SwiftImport<User>.importObject
                  <^> context
                  <*> JSONObject -<< JSONObjectWithData -<< data
} catch {
    // handle error
}