//Realm BASIC migration setup
   let config = Realm.Configuration(
     // Set the new schema version. This must be greater than the previously used
     // version (if you've never set a schema version before, the version is 0).
     schemaVersion: 4,

     // Set the block which will be called automatically when opening a Realm with
     // a schema version lower than the one set above
     migrationBlock: { migration, oldSchemaVersion in
       // We haven’t migrated anything yet, so oldSchemaVersion == 0
       if (oldSchemaVersion < 3) {
         // Nothing to do!
         // Realm will automatically detect new properties and removed properties
         // And will update the schema on disk automatically
       }
   })

   // Tell Realm to use this new configuration object for the default Realm
   Realm.Configuration.defaultConfiguration = config

   // Now that we've told Realm how to handle the schema change, opening the file
   // will automatically perform the migration
   let realm = try! Realm()
   print(realm.path)

class User: Object {

//MARK - Properties
  dynamic var id:Int = 0
  dynamic var email:String = ""
  ...
  var skills = List<Skill>()

  override static func primaryKey() -> String? {
    return "id"
  }
...  

import Foundation
import RealmSwift
import ObjectMapper

class User: Object, Mappable {

//MARK - Properties
  dynamic var id:Int = 0
  dynamic var email:String = ""
  ...
  var skills = List<Skill>()

  override static func primaryKey() -> String? {
    return "id"
  }

//MARK - Initializers
  required convenience init?(_ map: Map) {
    self.init()
  }

//MARK - Mapping
  func mapping(map: Map) {
    id <- map["id"]
    email <- map["email"]
    ...
    let realm = try! Realm()    
    var skillIdsArray = [Int]()
    skillIdsArray <- map["skill_ids"]
    for skillId in skillIdsArray {
      ...//Here there are some other instructions to verify if the skill was effectively in Realm database
      skills.append(skill)
    }
  }

}

public enum MyProjectAPI {
  case GetAllUsers
  case EditUser(user: AnyObject)
}

public var path: String {
    switch self {
    case .GetAllUsers:
      return "/users"
    case .EditUser:
      return "/users/id"
    }
  }

//Request type
  public var method: Moya.Method {
    switch self{
    case .EditUser:
      return .PUT
    default:
      return .GET
    }
  }

//Possible passed parameters
  public var parameters: [String: AnyObject]? {
    switch self {
    case .EditUser(let user):
      let currentUser: User = user as! User
      //Closure for skills id array
      let skills_ids = {() -> [Int] in
        var skills_ids = [Int]()
        for skill in currentUser.skills {
          let skill_id = (skill as Skill).id
          skills_ids.append(skill_id)
        }
        return skills_ids
      }
      return [
        "user" : [
          "id" : currentUser.id,
          "email" : currentUser.email,
          ...
          "skill_ids" : skills_ids()
        ]
      ]
    default:
      return nil
    }
  }

public var sampleData: NSData {
    switch self {
    case .GetAllUsers:
      return sampleResponse("UserTest")
    }
}

func sampleResponse(filename: String) -> NSData! {
  let bundle = NSBundle.mainBundle()
  let path = bundle.pathForResource(filename, ofType: "json")
  print("********* SAMPLE RESPONSE *********")
  return NSData(contentsOfFile: path!)
}

let endpointsClosure = { (target: MyAPI) -> Endpoint<MyAPI> in
  let endpoint: Endpoint<MyAPI> = Endpoint<MyAPI>(
    URL: url(target),
    sampleResponseClosure: {.NetworkResponse(200, target.sampleData)},
    method: target.method,
    parameters: target.parameters)
    return endpoint.endpointByAddingHTTPHeaderFields([
      "Accept" : Constants.acceptHTTPHeaderField,
      "Accept-Language" : Constants.acceptLanguageHTTPHeaderField,
      "Client-Version" : Constants.clientVersionHTTPHeaderField,
      "If-None-Match" : getETagOrLastModifiedParameter(target,true),
      "If-Modified-Since" : getETagOrLastModifiedParameter(target,false),
      "X-API-Username" : Constants.getCurrentUser().username,
      "X-API-Token" : UICKeyChainStore.stringForKey("token")])
}

class MyProvider {

  private let provider:MoyaProvider<MyAPI>

  private init(){
    self.provider = MoyaProvider<MyAPI>(endpointClosure: endpointsClosure)
  }
  ...

func getAllElementsOfType(type: MyAPI) {
    provider.request(type) { (result) -> () in
      switch result {
      case let .Success(response):
        do {
            if response.statusCode == 200 || response.statusCode == 304  {
            //Handle response with ObjectMapper
            let responseJSON:AnyObject = try response.mapJSON()
            var elementsFromJSON = []
            switch type {
            case .GetAllUsers:
              guard let usersFromJSON: Array<User> = Mapper<User>().mapArray(responseJSON["users"])! else {
                print("*********** NO getAllUsers DATA ***********")
                break
              }
              elementsFromJSON = usersFromJSON
              ...
            }
            try! self.realm.write({ () -> Void in
              for element in elementsFromJSON {
                switch type {
                case .GetAllUsers:
                  self.realm.add(element as! User, update: true)
                default:
                  break
                }
              }
            })
            ...