ignore null object in array when parse with Codable swift

Question

i'm parsing this API with swift Codable

"total": 7,
"searchResult": [
    null,
    {
        "name": "joe"
        "family": "adam"
    },
    null,
    {
        "name": "martin"
        "family": "lavrix"
    },
    {
        "name": "sarah"
        "family": "mia"
    },
    null,
    {
        "name": "ali"
        "family": "abraham"
    }
]

with this PaginationModel:

class PaginationModel<T: Codable>: Codable {
    var total: Int?
    var data: T?

    enum CodingKeys: String, CodingKey {
        case total
        case data = "searchResult"
    }

    required init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        self.total = try container.decodeIfPresent(Int.self, forKey: .total)
        self.data = try container.decodeIfPresent(T.self, forKey: .data)
    }
}

and User Model:

struct User: Codable {
    var name: String?
    var family: String?
}

i call jsonDecoder like this to parse API json:

let responseObject = try JSONDecoder().decode(PaginationModel<[User?]>.self, from: json)

now my problem is null in searchResult Array. it parsed correctly and when i access to data in paginationModel i found null in array.

how can i ignore all null when parsing API, and result will be an array without any null

yes with this ?, it normally parsed to null. i want an array without null object — Sajjad
– Sajjad, Commented Mar 15, 2019 at 13:43

Sulthan · Accepted Answer · 2019-03-15 15:14:31Z

4

In the first place, I would advise to always consider PaginationModel to be composed from arrays. You don't have to pass [User] as the generic type, you can just pass User. Then the parser can use the knowledge that it parses arrays and handle null automatically:

class PaginationModel<T: Codable>: Codable {
    var total: Int?
    var data: [T]?

    enum CodingKeys: String, CodingKey {
        case total
        case data = "searchResult"
    }

    required init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        self.total = try container.decodeIfPresent(Int.self, forKey: .total)

        self.data = (try container.decodeIfPresent([T?].self, forKey: .data))?.compactMap { $0 }
    }
}

You might want to remove optionals here and use some default values instead:

class PaginationModel<T: Codable>: Codable {
    var total: Int = 0
    var data: [T] = []

    enum CodingKeys: String, CodingKey {
        case total
        case data = "searchResult"
    }

    required init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        self.total = (try container.decodeIfPresent(Int.self, forKey: .total)) ?? 0

        self.data = ((try container.decodeIfPresent([T?].self, forKey: .data)) ?? []).compactMap { $0 }
    }
}

edited Mar 15, 2019 at 15:14

answered Mar 15, 2019 at 14:51

Sulthan

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7 Comments

Rob Napier Over a year ago

I'd also recommend making total (likely) and data (definitely) required rather than Optional. That will simplify this a lot by getting rid of the decodeIfPresent. (Similarly, are name and family really Optional? Is there a difference between "missing" and empty string?)

Sulthan Over a year ago

@RobNapier Very true.

Sajjad Over a year ago

this is exactly what i want. tnx @Sulthan

Sajjad Over a year ago

@RobNapier i agree with you. but our server side developer said that if suddenly they came with null value ( because of bugs from server or ... ) you must handle it

Rob Napier Over a year ago

Even so, you're better off making them mandatory, and defaulting them to empty strings in the decoder so you don't have to treat them as optional everywhere in the program.

|

vadian · Accepted Answer · 2019-03-15 14:00:19Z

1

Simple solution, filter data after decoding

let responseObject = try JSONDecoder().decode(PaginationModel<[User?]>.self, from: data)
responseObject.data = responseObject.data?.filter{$0 != nil}

answered Mar 15, 2019 at 14:00

vadian

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4 Comments

Sajjad Over a year ago

this can be a solution, but i'm looking for a better solution. especially all thing to be done in PaginationModel

vadian Over a year ago

The problem is that generic T can be a single object as well as an array. The best solution is to filter the null values already on the server.

user28434'mstep Over a year ago

@Sajjad, PaginationModel currently doesn't have enough information about actual type used in generic, you would have to pass info that you're actually looking for Array and then in init(from decoder: Decoder) decode it as [T?] first and then compactMap it to [T] and save into property.

Sajjad Over a year ago

ok. if i change data : T? to data: [T?], then can i handle it?

E.Coms · Accepted Answer · 2019-03-15 14:46:54Z

0

You may add an array type check within decode :

  required init(from decoder: Decoder) throws {
    let container = try decoder.container(keyedBy: CodingKeys.self)
    self.total = try container.decodeIfPresent(Int.self, forKey: .total)
    self.data = try container.decodeIfPresent(T.self, forKey: .data)

    //add the following:
    if let array =  self.data as? Array<Any?> {
        self.data = ( array.compactMap{$0} as? T)
    }
}

answered Mar 15, 2019 at 14:46

E.Coms

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Comments

Sean Mayes · Accepted Answer · 2021-08-07 15:12:13Z

0

Note, you can just define the decodable variable that may be null/nil as [Float?] (or whatever type), with the optional '?' inside the array brackets.

answered Aug 7, 2021 at 15:12

Sean Mayes

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