Converting JSON to ManagedObject for optional parameters in swift

Question

I've json data in below format:

{
    "AvailToDate": "2016-12-31 00:00:00.0",
    "CompanyName": "Google",
    "ShowroomName": "Mobile Phones",
    "OwnerUserId": "OID1544234",
    "PartyId": "APL026306123",
    "Currency": "USD",
    "ProductCount": 10,
    "AvailFromDate": "2016-12-20 00:00:00.0",
    "MaxPrice": 10,
    "MinPrice": 1,
    "ShowroomId": 11904,
    "AccessStatus": "Open"
  }

I'm able to convert array of above objects into array of Dictionary objects. Then I am converting the dictionary object to core data entity.

Here's my code to convert the Dictionary object to ManagedObject

let showroom = Showroom(context: bgContext)

showroom.availableFromDate = (tShowroom[kAvailFromDate] as? String)?.toDate()
showroom.minPrice = tShowroom[kMinPrice] as? Float
showroom.showroomID = tShowroom[kShowroomId] as! Int32
showroom.accessStatus = tShowroom[kAccessStatus] as? String
showroom.availableToDate = (tShowroom[kAvailToDate] as? String)?.toDate()
showroom.companyName = tShowroom[kCompanyName] as? String
showroom.showroomName = tShowroom[kShowroomName] as? String
showroom.ownerID = tShowroom[kOwnerUserId] as? String
showroom.partyID = tShowroom[kPartyId] as? String
showroom.currency = tShowroom[kCurrency] as? String
showroom.productsCount = tShowroom[kProductCount] as! Int32
showroom.maxPrice = tShowroom[kMaxPrice] as? Float

If some of the parameters are missing JSON received, how can we parse the object. Do I have to set all the parameters in my ManagedObject as Optional? I don't want to use "if let" or "guard" for every parameter. What's the best way to achieve it?

Answer 1

I would recommend to set every parameters to optional on your Showroom model. It is much safer this way.

Also, you could be introducing some transforming related class for your models, where you would be doing the guard - if let checks, and you would just deal with errors.

Like the following:

import Foundation
import UIKit

enum DictionaryParseError: Error {
    case missingKey
    case invalidType
}

extension Dictionary where Key: ExpressibleByStringLiteral {

    // You are expecting an optinal string
    func string(key: Key) -> String? {
        return self[key] as? String
    }

    // You are expecting an optinal float
    func float(key: Key) -> Float? {
        return self[key] as? Float
    }

    // You are expecting a string
    func requiredString(key: Key) throws -> String {
        let string = try self.requiredValue(key) as String
        return string
    }

    // You are expecting a float
    func requiredFloat(key: Key) throws -> Float {
        let float = try self.requiredValue(key) as Float
        return float
    }

    private func requiredValue<Type>(_ key: Key) throws -> Type {
        guard let value = self[key] else {
            throw DictionaryParseError.missingKey
        }
        guard let typedValue = value as? Type else {
             throw DictionaryParseError.invalidType
        }
        return typedValue
    }
}

Answer 2

You can simply add a "default value" to the variable using the ?? syntax

let say you want to set the min price to 10.2 IF there is not a value return from the json, do it like this:

showroom.minPrice = tShowroom[kMinPrice] as? Float ?? 10.2

Or for string:

showroom.accessStatus = tShowroom[kAccessStatus] as? String ?? "Default String"

Answer 3

If you don't have a value for one of the managed object properties, you have two options:

• Don't set any value for the property, leaving it as nil. That requires the property be declared as optional in the data model. Optional here specifically means that the property is allowed to have no value.
• Set some default value when you don't have a specific value to assign.

Which choice you make depends entirely on how you plan to use your data and on whether any reasonable default values exist. You don't have to handle every property the same way.