Decoding optional values in JSON - Swift 4

Question

I've read read many tutorials and searched for answers here on SO;

Decoding Nested JSON with Optional Values Swift 4

Swift 4 Not decoding JSON optional properly

Decoding optionals doesn't seem problematic using below code. Obviously I'm doing something wrong, but what is it!?

Part of my code:

struct ProductInfo: Codable {
    var name: String?
    let images: [Image]
    var ingredients: String?
    let origin: [Origin]
    let producer: Producer

    enum CodingKeys: String, CodingKey {
        case name = "Artikelbenamning"
        case images = "Bilder"
        case ingredients = "Ingrediensforteckning"
        case origin = "Tillverkningslander"
        case producer = "Varumarke"
    }

    init(from decoder: Decoder) throws {

        let values = try decoder.container(keyedBy: CodingKeys.self)

        name = try? values.decodeIfPresent(String.self, forKey: .name)!
        images = try values.decodeIfPresent([Image].self, forKey: .images)!
        ingredients = try? values.decodeIfPresent(String.self, forKey: .ingredients)!
        origin = try values.decodeIfPresent([Origin].self, forKey: .origin)!
        producer = try values.decodeIfPresent(Producer.self, forKey: .producer)!
    }
}

The app queries a products database. Following json is returned when a product doesn't exist. App crashes when trying to decode nil name ("Artikelbenamning in json) in init(from:).

{
    "GTIN": null,
    "TillverkarensArtikelnummer": null,
    "Artikelbenamning": null,
    "RegleratProduktnamn": null,
    "Forvaringsinstruktion": null,
    "Variabelmattsindikator": false,
    "Bruttovikt": null,
    "Bredd": null,
    "Djup": null,
    "Hojd": null,
    "Returemballage": false,
    "FarligtGodsKod": null,
    "FarligtGodsKlass": null,
    "FarligtGodsForpackningsgrupp": null,
    "GPCKod": null,
    "GiltigFROM": null,
    "Publiceringsdatum": null,
    "FakturerbarEnhet": false,
    "Slutdatum": null,
    "GiltighetsdatumPris": null,
    "Tillganglighetstidpunkt": null,
    "SistaTillganglighetstidpunkt": null,
    "SkapadDatum": null,
    "SenastAndradDatum": null,
    "Flampunkt": null,
    "KodBegransadMangd": null,
    "OfficiellTransportbenamning": null,
    "OspecificeradTransportbenamning": null,
    "TunnelrestriktionADR": null,
    "KlassificeringskodFarligtgods": null,
    "Transportkategori": null,
    "Konsumentartikel": false,
    "BestallningsbarForpackning": false,
    "RabattOlaglig": null,
    "Garantiloptid": 0,
    "Konsumentdatum": null,
    "Tjanst": false,
    "Sasongsindikator": null,
    "Engangskop": null,
    "AntalReturnerbaraEnheter": 0,
    "Staplingsriktning": null,
    "Staplingstyp": null,
    "MaxTransportTemperatur": 0.0,
    "MinTransportTemperatur": 0.0,
    "Anvandningsinstruktioner": null,
    "HallbarhetEfterOppning": 0,
    "Riskfras": null,
    "KodlistutgivareRiskfras": null,
    "Klassificeringssystem": null,
    "FarligtGodsBegransadMangd": null,
    "FarligtGodsOvrigInfo": null,
    "FarligtGodsSarbestammelser": null,
    "T3495_Artikelavisering": null,
    "T4032_TypAvUtgangsdatum": null,
    "T3742_ForstaLeveransdatum": null,
    "Undervarumarke": null,
    "Niva": null,
    "Produktbladslank": null,
    "KompletterandeProduktklass": null,
    "T4200_AllmänPubliceringstidpunkt": null,
    "T3848_TypAvTryckkanslighet": null,
    "Varningsetiketter": [],
    "Sasongskoder": [],
    "Produktklasser": [],
    "MaskinellMarkningar": [],
    "Bilder": [],
    "ReferenserTillAndraArtiklar": [],
    "MSRKritierier": [],
    "Kravspecifikationer": [],
    "Receptlinks": [],
    "Allergener": [],
    "Markningar": [],
    "Ingredienser": [],
    "Tillagningsinformation": [],
    "Tillverkningslander": [],
    "Naringsinfo": [],
    "Serveringsforslag": [],
    "Diettyper": [],
    "Tillagningsmetoder": [],
    "Farger": [],
    "VillkorForsaljning": [],
    "Varumarke": {
        "Varumarke": null,
        "AgareGLN": null,
        "AgareNamn": null,
        "Tillverkare": {
            "Namn": null,
            "EAN": null
        }
    },
    "Nettoinnehall": [],
    "Kontakter": [],
    "Faroangivelser": [],
    "Sakerhet": [],
    "Forpackningar": [],
    "Tillsatser": [],
    "Substanser": [],
    "Fangstzoner": [],
    "Marknadsbudskap": null,
    "KortMarknadsbudskap": null,
    "Komponenter": null
}

vadian · Accepted Answer · 2019-01-22 17:45:56Z

2

The API decodeIfPresent is pointless in this case because the key does exist.

An existing key with null value and a missing key are two different situations.

And never force unwrap in the init(from decoder method.

There are two options:

Delete the entire init method then the optional struct members handle the null values.

Use regular decode and ignore the error

name = try? values.decode(String.self, forKey: .name)

answered Jan 22, 2019 at 17:45

vadian

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5 Comments

Dan Abnormal Over a year ago

Thanks for your response. Sorry, newbie here, what exactly do you mean bt your option 1?

vadian Over a year ago

I mean what I wrote: Delete the init(from decoder method. The protocol extension provides a synthesized one.

Dan Abnormal Over a year ago

Ok. I will try and get back to you.

Dan Abnormal Over a year ago

Curious, can you tell me why it crashed?

vadian Over a year ago

Because try? returns an optional and if there is is no string (or one of the other types) and you force unwrap it, it crashes. Please read the third paragraph once more.

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