swift4编码解码，用于嵌套json解析的模型类

Question

I have a model class of swift which was created based on a nested json response, it follows like below

struct RootClass : Codable {
    let details : String?
    let itemCount : Int?
    let list : [List]?

    enum CodingKeys: String, CodingKey {
        case details = "Details"
        case itemCount = "ItemCount"
        case list = "List"
    }

    init(from decoder: Decoder) throws {
        let values = try decoder.container(keyedBy: CodingKeys.self)
        details = try values.decodeIfPresent(String.self, forKey: .details)
        itemCount = try values.decodeIfPresent(Int.self, forKey: .itemCount)
        list = try values.decodeIfPresent([List].self, forKey: .list)
    }
}
struct List : Codable {

    let companyID : Int?
    let employeeCount : Int?
    let employeeUser : EmployeeUser?

    enum CodingKeys: String, CodingKey {
        case companyID = "CompanyID"
        case employeeCount = "EmployeeCount"
        case employeeUser = "EmployeeUser"
    }

    init(from decoder: Decoder) throws {
        let values = try decoder.container(keyedBy: CodingKeys.self)
        companyID = try values.decodeIfPresent(Int.self, forKey: .companyID)
        employeeCount = try values.decodeIfPresent(Int.self, forKey: .employeeCount)
        employeeUser = try EmployeeUser(from: decoder)
    }
}
struct EmployeeUser : Codable {
    let mobileNumber : String?
    let name : String?

    enum CodingKeys: String, CodingKey {
        case mobileNumber = "MobileNumber"
        case name = "Name"
    }

    init(from decoder: Decoder) throws {
        let values = try decoder.container(keyedBy: CodingKeys.self)
        mobileNumber = try values.decodeIfPresent(String.self, forKey: .mobileNumber)
        name = try values.decodeIfPresent(String.self, forKey: .name)
    }

}

and my json response is

{
    "Details": null,
    "List": [
        {
            "CompanyID": 140,
            "EmployeeUser": {
                "Name": " raghu2",
                "MobileNumber": "8718718710"
            },
            "EmployeeCount": 0
        },
        {
            "CompanyID": 140,
            "EmployeeUser": {
                "Name": "new emp reg",
                "MobileNumber": "1"
            },
            "EmployeeCount": 0
        }
    ],
    "ItemCount": 0
}

I am trying to parse it like

guard let data = data else { return }
        do {
            let decoder = JSONDecoder()
            let gitData = try decoder.decode(RootClass.self, from: data)
            print(gitData.itemCount ?? "")
            print(gitData.list![0].employeeUser?.mobileNumber ?? "")
        }
        catch let err {
            print("Err", err)
        }

I am able to get the values of root class and list but I am getting nil values under employee user section.

Answer 1

Your code a few problems:

• All your keys are optional. The vendor API will tell you what keys are always present and which one are optional. Follow that.

• decodeIfPresent will silently fail if it cannot decode a key. When debugging your app, you want things to fail with a bang so you can fix the error before going to production.

• You wrote way more code than needed. All those init(from decoder: ) functions are not needed. One one did cause your problem.

Your problem was caused by this line:

struct List : Codable {
    init(from decoder: Decoder) throws {
        ...
        employeeUser = try EmployeeUser(from: decoder)
    }
}

You are asking Swift to decode to same JSON to a List and a EmployeeUser object. Obviously, that's not valid. But when you decode list inside RootClass, you call decodeIfPresent :

// In Rootclass
list = try values.decodeIfPresent([List].self, forKey: .list)

This call silently failed and you never knew what the problem was!

---

Solution

Change how you initialize employeeUser to this:

employeeUser = try values.decodeIfPresent(EmployeeUser.self, forKey: .employeeUser)

But the most elegant solution is to delete all those init(from decoder: ) . The compiler will synthesize them for you.

And finally, fix those optionals!