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I'm using Alamofire, Objectmapper, Realm and everything is working beside one thing: I can't map nested objects.

class Voting: Object, Mappable 

 dynamic var votingID: String = ""
 dynamic var question: String = ""
 var votingOptions = List<VotingOption>()

 required convenience init?(_ map: Map) 
 self.init()
 

 func mapping(map: Map) 
 votingID <- map["id"]
 question <- map["question"]
 votingOptions <- map["votingOptions"]
 

 override class func primaryKey() -> String 
 return "votingID"
 


class VotingOption: Object, Mappable

 dynamic var optionID: String = ""
 dynamic var text: String = ""


 required convenience init?(_ map: Map) 
 self.init()
 

 func mapping(map: Map) 
 optionID <- map["id"]
 text <- map["optionText"]
 

 override class func primaryKey() -> String 
 return "optionID"
 

The JSON that I'm trying to map is:

 "Voting": [
 
 "question": "Which option do yo prefer?",
 "id": "7f073efd-6f3d-43f2-9fe4-5cad683b77a2",
 "votingOptions": [
 
 "optionText": "Option 3",
 "id": "3bc0a618-8791-4862-a7fd-5f2df464697d"
 ,
 
 "optionText": "Option 1",
 "id": "84c6a830-814b-40c8-a252-c074be5d689a"
 ,
 
 "optionText": "Option 2",
 "id": "8872ef6f-fc70-445a-802e-d39944006467"
 
 ]
 
 ]

The mapping funktion in VotingOption never gets called.

The old ListTransform solution no longer works in Swift 3.

This is what I'm using now; put this in a file called, ListExtensions.swift, for example.

import Foundation
import ObjectMapper
import RealmSwift

/// Maps object of Realm's List type
func <- <T: Mappable>(left: List<T>, right: Map)

 var array: [T]?

 if right.mappingType == .toJSON 
 array = Array(left)
 

 array <- right

 if right.mappingType == .fromJSON 
 if let theArray = array 
 left.append(objectsIn: theArray)
 
 

This allows you to simply use it like this:

class Parent: Object, Mappable 
 dynamic var id: Int = 0
 var children = List<Child>()

 required convenience init?(_ map: Map) 
 self.init()
 

 func mapping(map: Map) 
 id <- map["id"]
 children <- map["children"]
 

The problem you're seeing is due to ObjectMapper having no knowledge of Realm's List type. It is not aware that it is a collection type, and that it must be mutated in place rather than being assigned to. You can see discussion of this, including some suggested workarounds, in ObjectMapper GitHub issue #143.

Note also that any List properties on Object subclasses should be declared with let rather than var.

class ListTransform<T:RealmSwift.Object> : TransformType where T:Mappable 
 typealias Object = List<T>
 typealias JSON = [AnyObject]

 let mapper = Mapper<T>()

 func transformFromJSON(_ value: Any?) -> Object? 
 let results = List<T>()
 if let objects = mapper.mapArray(JSONObject: value) 
 for object in objects 
 results.append(object)
 
 
 return results
 

 func transformToJSON(_ value: Object?) -> JSON? 
 var results = [AnyObject]()
 if let value = value 
 for obj in value 
 let json = mapper.toJSON(obj)
 results.append(json as AnyObject)
 
 
 return results
 

Then in your model something like this.

class Parent: Object, Mappable 
 dynamic var id: Int = 0
 var children = List<Child>()

 required convenience init?(_ map: Map) 
 self.init()
 

 func mapping(map: Map) 
 id <- map["id"]
 child <- (map["children"], ListTransform<Child>())
 

You can extend ObjectMapper for Realm.List type with a operator function like as:

public func <- <T: Object where T: Mappable, T: JSPrimaryKey>(left: List<T>, right: Map) 
 if right.mappingType == MappingType.FromJSON 
 if let value = right.currentValue 
 left.removeAll()
 if let json = value as? [[String : AnyObject]] 
 let objs = RealmS().add(T.self, json: json)
 left.appendContentsOf(objs)
 
 
 

Try yourself.

ObjectMappper + Realm List type