Swift ObjectMapper type inference

Question

Dear Stackoverflowers,

I have a hindrance regarding using ObjectMapper, so lets get straight to the point.

I'm saving models as a temporary record in a SQLite table, in JSON form. Each model has a Type field that uniquely identifies to which Model type it maps to.

For instance, if we have Models Dog, Cat, Mouse conforming to the Animal protocol, there's a equivalent AnimalType (DogType, CatType, MouseType) enum, which is also a field in each of the Models. Once saved to the database, I'm having trouble figuring out a elegant way of mapping the JSON loaded from the database to an actual instance of a Model class.

What I'm currently doing is converting the JSON via NSJSONSerialization into a JSON dictionary and querying the dictionary for the Type. Once the Type's found, I switch through all Types, instantiating a related Mapper object and attempting to deserialize the object. I feel this is a brute-force approach and was thinking there might be a better way of approach this problem.

Conclusive :

Models : Dog, Cat, Mouse (conforming to Animal, has AnimalType requirement)

Enums : AnimalType (DogType, CatType, MouseType)

Problem : How to determine and correctly instantiate a Mapper object to deserialize the loaded JSON into a instance, other than manually inspecting each Type and instantiating a correct mapper.

enum AnimalType {
    case Dog
    case Cat
    case Mouse
}

protocol Animal {
    var animalType: AnimalType { get }
}

struct Dog: Animal {
    var animalType = AnimalType.Dog
}

struct Cat: Animal {
    var animalType = AnimalType.Cat
}

struct Mouse: Animal {
    var animalType = AnimalType.Mouse
}

Answer 1

import ObjectMapper

enum AnimalType : String {
    case Cat = "Cat"
    case Dog = "Dog"
    case Mouse = "Mouse"
}

class Animal: StaticMappable, Mappable {
    var animalType: AnimalType?

    required init?(_ map: Map) {}

    init() {}

    func mapping(map: Map) {
        animalType <- (map["animalType"], EnumTransform<AnimalType>())
    }

    static func objectForMapping(map: Map) -> BaseMappable? {
        let typeString: String? = map["animalType"].value()
        if let typeString = typeString {
            let animalType: AnimalType? = AnimalType(rawValue: typeString)
            if let animalType = animalType {
                switch(animalType) {
                    case AnimalType.Cat: return Cat()
                    case AnimalType.Dog: return Dog()
                    case AnimalType.Mouse: return Mouse()
                }
            }
        }
        return Animal()
    }
}

class Cat: Animal {
    var purr: String?

    required init?(_ map: Map) {
        super.init(map)
    }

    override init() {
        super.init()
    }

    override func mapping(map: Map) {
        super.mapping(map)

        purr <- map["purr"]
    }
}

class Dog: Animal {
    var bark: String?
    var bite: String?

    required init?(_ map: Map) {
        super.init(map)
    }

    override init() {
        super.init()
    }

    override func mapping(map: Map) {
        super.mapping(map)

        bark <- map["bark"]
        bite <- map["bite"]
    }
}

class Mouse: Animal {
    var squeak: String?

    required init?(_ map: Map) {
        super.init(map)
    }

    override init() {
        super.init()
    }

    override func mapping(map: Map) {
        super.mapping(map)

        squeak <- map["squeak"]
    }
}

class Owner : Mappable {
    var name: String?
    var animal: Animal?

    required init?(_ map: Map) {}

    func mapping(map: Map) {
        name <- map["name"]
        animal <- map["animal"]
    }
}

let catJson = "{\"animalType\":\"Cat\",\"purr\":\"rrurrrrrurrr\"}"
let cat = Mapper<Cat>().map(catJson)
if let cat = cat {
    let catJSONString = Mapper().toJSONString(cat, prettyPrint: false)
}

let ownerJson = "{\"name\":\"Blofeld\", \"animal\":{\"animalType\":\"Cat\",\"purr\":\"rrurrrrrurrr\"}}"
let owner = Mapper<Owner>().map(ownerJson)
if let owner = owner {
    let ownerJSONString = Mapper().toJSONString(owner, prettyPrint: false)
}

I wrote this while looking for a Swift equivalent of @JsonSubTypes from Jackson for polymorphic mapping of JSON subclasses.