Swift 4 Decodable - No value associated with key CodingKeys

Question

I'm decoding a JSON response in my Swift App, and the code used to work till it decided to stop working.

this is my json reposnse

{
    "foods": [
        {
            "food_name": "Milk Chocolate",
            "brand_name": "Snickers",
            "serving_weight_grams": 41.7,
            "nf_calories": 212.3,
            "nf_total_fat": 11.6,
            "nf_saturated_fat": 4,
            "nf_total_carbohydrate": 22.7,
            "nf_protein": 3.9
        }
    ]
}

And this is the code to decode my json

let task = URLSession.shared.dataTask(with: request) { (data, response, error) in
        guard let data = data else { return }
        
        print(String(data: data, encoding: .utf8)!)
        do {
            //Decode dataResponse received from a network request
            let decoder = JSONDecoder()
            let foods = try decoder.decode(JSONFoods.self, from: data) //Decode JSON Response Data
            
            self.jsonfood = foods.JSONFood[0]
            print(self.jsonfood!)
            
        } catch let parsingError {
            print("Error", parsingError)
        }
        
    }
    task.resume()

And my Structs are

struct JSONFoods: Decodable {
var JSONFood: [JSONFood]    
}

struct JSONFood: Decodable{
var food_name: String
var brand_name: String
var nf_calories: Int
var nf_protein: Int
var nf_total_fat: Int
var nf_total_carbohydrate: Int
var serving_weight_grams: Int
}

And the error message I get is this

keyNotFound(CodingKeys(stringValue: "JSONFood", intValue: nil), Swift.DecodingError.Context(codingPath: [], debugDescription: "No value associated with key CodingKeys(stringValue: "JSONFood", intValue: nil) ("JSONFood").", underlyingError: nil))

And if i get replace decode(JSONFoods.self, from: data) with decode(JSONFood.self, from: data) I get this error message

keyNotFound(CodingKeys(stringValue: "food_name", intValue: nil), Swift.DecodingError.Context(codingPath: [], debugDescription: "No value associated with key CodingKeys(stringValue: "food_name", intValue: nil) ("food_name").", underlyingError: nil))

I searched everywhere with no luck, any help is very appreciated

For me, it is because some fields type in data model is not set to optional, which could be nil. When I set those fields to optional type, the error is gone. However, our API doc is poor, it doesn't mention which field could be nil. — Zhou Haibo, Sep 14 '22 at 10:35

Shehata Gamal · Accepted Answer · 2019-04-07T18:44:56.630

You need

struct Root: Codable {
    let foods: [Food]
}

struct Food: Codable {
    let foodName: String?
    let  brandName: String
    let servingWeightGrams, nfCalories, nfTotalFat: Double
    let nfSaturatedFat: Int
    let nfTotalCarbohydrate, nfProtein: Double

    enum CodingKeys: String, CodingKey {
        case foodName = "food_name"
        case brandName = "brand_name"
        case servingWeightGrams = "serving_weight_grams"
        case nfCalories = "nf_calories"
        case nfTotalFat = "nf_total_fat"
        case nfSaturatedFat = "nf_saturated_fat"
        case nfTotalCarbohydrate = "nf_total_carbohydrate"
        case nfProtein = "nf_protein"
    }
}

First : you make JSONFood while it should be foods

Second :food_name doesn't exist in current json root so this will fail

let foods = try decoder.decode(JSONFoods.self, from: data) //Decode JSON Response Data

In case to take advantage of convertFromSnakeCase

let str = """

{"foods":[{"food_name":"Milk Chocolate","brand_name":"Snickers","serving_weight_grams":41.7,"nf_calories":212.3,"nf_total_fat":11.6,"nf_saturated_fat":4,"nf_total_carbohydrate":22.7,"nf_protein":3.9}]}

"""

    do {
        let res = JSONDecoder()
        res.keyDecodingStrategy = .convertFromSnakeCase
        let ss = try res.decode(Root.self, from:Data(str.utf8))
        print(ss)
    }
    catch {
        print(error)
    }

struct Root: Codable {
    let foods: [Food]
}

struct Food: Codable {
    let foodName: String?
    let  brandName: String
    let servingWeightGrams, nfCalories, nfTotalFat: Double
    let nfSaturatedFat: Int
    let nfTotalCarbohydrate, nfProtein: Double
}

There is no need to rename the `JSONFoods` struct to `Root`. — rmaddy, Apr 07 '19 at 18:24
i do it in case there are multiple structs for highlighting base model — Shehata Gamal, Apr 07 '19 at 18:26
The second error in the question occurs because the OP decodes the child struct `JSONFood` as root object. It has nothing to do that `food_name` could be missing. And why don't you suggest `.convertFromSnakeCase` strategy to get rid of the `CodingKeys`? — vadian, Apr 07 '19 at 18:32
i just edit that before the comment :) , and yes i agree snake case is better but dynamic site generation may not take it inconsideration for now =D — Shehata Gamal, Apr 07 '19 at 18:40

Swift 4 Decodable - No value associated with key CodingKeys

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