How to Properly Map JSON Properties to Model Properties in Realm.Create

How should I assign my data models to map the JSON using Alamofire?

Add a method to convert from FriendModel to UserModel:

struct UserModel {
    init(friend: FriendModel) {
        id = friend.id
        userFirstName = friend.firstName
        userSurname = friend.lastName
        ... // assign all the other fields as needed
    }
}

Then use it to convert your results:

friendsAPI.getFriends { [weak self] apiFriends in
    self?.friends0 = apiFriends.map({ UserModel(friend: $0) })
}

Here it is an init method, but feel free to put it in a normal func like func userFromFriend(_ friend: FriendModel) -> UserModel, and put that func wherever you want.

Realm `description` property behaving differently to other properties

By creating a description property, you're overriding the -description method on NSObject that's used to print an object's contents when using NSLog or println.

See https://stackoverflow.com/a/4718806/373262 for more details.

Realm create() cannot parse JSON string to NSDate?

That's correct. You cannot take a String containing a date and automatically map it to an NSDate property in Realm.

The easiest way to get around this, would be to deserialize your JSON data into a mutable dictionary, and then manually replace that specific String property with an NSDate value, generated from a NSDateFormatter object. Once that's done, you should be able to simply pass the dictionary to Realm to create the new Object in it.

This was previously discussed in a Realm GitHub issue: https://github.com/realm/realm-cocoa/issues/605

Nested Arrays throwing error in realm.create(value: JSON) for Swift

Unfortunately you can't just setup your Requirements model in a different way, which would allow you to directly map your JSON to Realm objects.

The init(value: AnyObject) initializer expects either a dictionary, where the keys are the names of your object properties, or an array, where the property values are ordered in the same like they are defined in your object model. This initializer is recursively called for related objects.

So to make that work, you will need to transform your JSON, so that you nest the string values into either dictionaries or arrays. In your specific case you could achieve that like seen below:

…
var jsonDict = json as! [String : AnyObject]
jsonDict["requirements"] = jsonDict["requirements"].map { ["value": $0] }
let exhibit = Exhibit(value: jsonDict)
…

Side Note

I'd recommend using singular names for your Realm model object classes (here Requirement instead Requirements) as each object just represent a single entity, even if you use them only in to-many relationships.

How to map a realm list of custom objects using Mappable protocol in Swift

Having a look at one of the Issues page on ObjectMapper's GitHub repo, it doesn't look like Realm List objects are properly supported yet.

That issue also lists a potential workaround for getting it to work for the time being, which I'll mirror here:

class MyObject: Object, Mappable {
    let tags = List<Tag>()

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

    func mapping(map: Map) {
        var tags: [Tag]?
        tags <- map["tags"]
        if let tags = tags {
            for tag in tags {
                self.tags.append(tag)
            }
        }
    }
}

Realm + Swift, nested JSON

In your JSON, ageRange is a dictionary, whereas the UserObject.ageRange property is a List<AgeRangeObject>. You have mismatched models.

You either need to update your models to reflect the structure of your JSON:

var ageRange = List<AgeRangeObject>()

becomes

dynamic var ageRange: AgeRangeObject? = nil

or vice versa, update your JSON to reflect the structure of your models:

{
  "gender" : "male",
  "id" : "123456789",
  "age_range" : [{
    "min" : 21
  }],
  "last_name" : "LastName" 
}