Realm + Codable. Serializer example (version 1)

JSONSerializer_v1.swift

import Foundation
import RealmSwift

class JSONSerializer {
    func serialize(input sourceName: String) {
        let path = Bundle.main.path(forResource: sourceName, ofType: nil)
        let url = URL(fileURLWithPath: path!)
        let jsonDecoder = JSONDecoder()
        do {
            let data = try Data(contentsOf: url)
            let json = try JSONSerialization.jsonObject(with: data, options: .allowFragments)
            guard json is [AnyObject] else {
                assert(false, "failed to parse")
                return
            }
            do {
                let cats = try jsonDecoder.decode([Cat].self, from: data)
                let realm = try! Realm()
                for cat in cats {
                    try! realm.write {
                        realm.add(cat)
                    }
                }
            } catch {
                print("failed to convert data")
            }
        } catch let error {
            print(error)
        }
    }
}