How can I store a Dictionary with RealmSwift?

Question

Considering the following model:

class Person: Object {
    dynamic var name = ""
    let hobbies = Dictionary<String, String>()
}

I'm trying to stock in Realm an object of type [String:String] that I got from an Alamofire request but can't since hobbies has to to be defined through let according to RealmSwift Documentation since it is a List<T>/Dictionary<T,U> kind of type.

let hobbiesToStore: [String:String]
// populate hobbiestoStore
let person = Person()
person.hobbies = hobbiesToStore

I also tried to redefine init() but always ended up with a fatal error or else.

How can I simply copy or initialize a Dictionary in RealSwift? Am I missing something trivial here?

Answer 1

Dictionary is not supported as property type in Realm. You'd need to introduce a new class, whose objects describe each a key-value-pair and to-many relationship to that as seen below:

class Person: Object {
    dynamic var name = ""
    let hobbies = List<Hobby>()
}

class Hobby: Object {
    dynamic var name = ""
    dynamic var descriptionText = ""
}

For deserialization, you'd need to map your dictionary structure in your JSON to Hobby objects and assign the key and value to the appropriate property.

Answer 2

I am currently emulating this by exposing an ignored Dictionary property on my model, backed by a private, persisted NSData which encapsulates a JSON representation of the dictionary:

class Model: Object {
    private dynamic var dictionaryData: NSData?
    var dictionary: [String: String] {
        get {
            guard let dictionaryData = dictionaryData else {
                return [String: String]()
            }
            do {
                let dict = try NSJSONSerialization.JSONObjectWithData(dictionaryData, options: []) as? [String: String]
                return dict!
            } catch {
                return [String: String]()
            }
        }

        set {
            do {
                let data = try NSJSONSerialization.dataWithJSONObject(newValue, options: [])
                dictionaryData = data
            } catch {
                dictionaryData = nil
            }
        }
    }

    override static func ignoredProperties() -> [String] {
        return ["dictionary"]
    }
}

It might not be the most efficient way but it allows me to keep using Unbox to quickly and easily map the incoming JSON data to my local Realm model.

Answer 3

I would save the dictionary as JSON string in Realm. Then retrive the JSON and convert to dictionary. Use below extensions.

extension String{
func dictionaryValue() -> [String: AnyObject]
{
    if let data = self.data(using: String.Encoding.utf8) {
        do {
            let json = try JSONSerialization.jsonObject(with: data, options: JSONSerialization.ReadingOptions.allowFragments) as? [String: AnyObject]
            return json!

        } catch {
            print("Error converting to JSON")
        }
    }
    return NSDictionary() as! [String : AnyObject]
} }

and

extension NSDictionary{
    func JsonString() -> String
    {
        do{
        let jsonData: Data = try JSONSerialization.data(withJSONObject: self, options: .prettyPrinted)
        return String.init(data: jsonData, encoding: .utf8)!
        }
        catch
        {
            return "error converting"
        }
    }
}