Repository Example.swift

import Foundation

class Model {
    let id: String
    let link: String
    let resizedLink: String
    
    func toDao() -> ModelDAO {
        let dao: ModelDAO = .init()
        // properties injection
        return dao
    }
}

class ModelDAO {
    @Persisted(primaryKey: true) var id: String
    @Persisted var link: String
    @Persisted var resizedLink: String
    
    func toModel() -> Model {
        return Model(id, link, resized)
    }
}

class Network {
    
    static func callAPI(completionHandler: @escaping (Result<Model, Error>) -> Void) {
        // ...
    }
}

class Database {
    static func saveModelDAO(_ model: Model) {
        realm.write {
            realm.add(model.toDao(), update: .all)
        }
    }
    
    static func getModelDAO() {
        realm.objects(ModelDAO.self).map { $0.toModel }
    }
}


class Repository {
    static func homePhotos(_ completion: @escaping (Result<[String], Error>) -> ()) {
        completion(.success(Database.getModelDAO()))
        Network.callAPI(completionHandler: {
            switch $0 {
            case let .success(model):
                Database.saveModelDAO(model)
                completion(Database.getModelDAO())
            case .failure: break
            }
        })
    }
}

class ViewController {
    init() {
        Repository.homePhotos { results in
            switch {
            case let .success(photos):
                
            }
        }
    }
}