Swift Codable - 如何编码自定义数组

Question

That's my JSON case

      {
                 "image_id": 11101,
                 "image_source_id": 9,
                 "image_author": "",
                 "image_copyright": "",
                 "image_format_list": [{
                         "image_format": {
                             "image_url": "https://static.musixmatch.com/images-storage/mxmimages/1/0/1/1/1/11101_2.jpg",
                             "image_format_id": 2,
                             "width": 150,
                             "height": 150
                         }
                     },
                     {
                         "image_format": {
                             "image_url": "https://static.musixmatch.com/images-storage/mxmimages/1/0/1/1/1/11101_16.jpg",
                             "image_format_id": 16,
                             "width": 451,
                             "height": 500
                         }
                     }
                 ]
             }

I correctly decode my custom object in two different classes: MXMImage & MXMImageFormat. But I can't figure out how to re-encode my object to rebuild the same JSON

That's my code:

    struct MXMImage : Decodable, Encodable, Equatable {
        let imageId: Int
        let imageSourceId: Int
        let imageAuthor: String?
        let imageCopyright: String?
        let imageFormatList: [MXMImageFormat]?

        enum CodingKeys: String, Swift.CodingKey {
            case imageId
            case imageSourceId
            case imageAuthor
            case imageCopyright
            case imageFormatList

            enum ImageFormatListKey: String, CodingKey {
                case imageFormat
            }
        }

        public init(from decoder: Decoder) throws {
            let container = try decoder.container(keyedBy: CodingKeys.self)
            imageId = try (container.decodeIfPresent(Int.self, forKey: .imageId) ?? 0)
            imageSourceId = try (container.decodeIfPresent(Int.self, forKey: .imageSourceId) ?? 0)
            imageAuthor = try? container.decodeIfPresent(String.self, forKey: .imageAuthor)
            imageCopyright = try? container.decodeIfPresent(String.self, forKey: .imageCopyright)

            var imagesFormatListContainer = try container.nestedUnkeyedContainer(forKey: .imageFormatList)
            var imagesList:[MXMImageFormat] = []
            while !imagesFormatListContainer.isAtEnd {
                let imageFormatContainer = try imagesFormatListContainer.nestedContainer(keyedBy: CodingKeys.ImageFormatListKey.self)
                let imageFormat = try? imageFormatContainer.decode(MXMImageFormat.self, forKey: .imageFormat)
                if let imageFormat = imageFormat {
                    imagesList.append(imageFormat)
                }
            }
            self.imageFormatList = imagesList
        }

        public func encode(to encoder: Encoder) throws {
            var container = encoder.container(keyedBy: CodingKeys.self)

            try container.encodeIfPresent(imageId, forKey: .imageId)
            try container.encodeIfPresent(imageSourceId, forKey: .imageSourceId)
            try container.encodeIfPresent(imageAuthor, forKey: .imageAuthor)
            try container.encodeIfPresent(imageCopyright, forKey: .imageCopyright)

            var imageContainer = container.nestedUnkeyedContainer(forKey: .imageFormatList)
            try imageFormatList?.forEach { imgFormat in
                var nested = imageContainer.nestedContainer(keyedBy: CodingKeys.ImageFormatListKey.self)
                let data = try imgFormat.encoded()
                try nested.encode(data, forKey: .imageFormat)

            }
        }
    }

In particular, I don't know how to re-indent my MXMImageFormat objects inside the key image_format and then encode the custom array. Is it possible to do that? Thanks in advance

Answer 1

Instead of nestedContainers you could decode/encode a [[String:MXMImageFormat]] array and map it

struct MXMImage : Codable, Equatable {
    let imageId: Int
    let imageSourceId: Int
    let imageAuthor: String?
    let imageCopyright: String?
    let imageFormatList: [MXMImageFormat]?

    private enum CodingKeys : String, CodingKey { case imageId,  imageSourceId,  imageAuthor, imageCopyright, imageFormatList}

    public init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        imageId = try container.decode(Int.self, forKey: .imageId)
        imageSourceId = try container.decode(Int.self, forKey: .imageSourceId)
        imageAuthor = try container.decodeIfPresent(String.self, forKey: .imageAuthor)
        imageCopyright = try container.decodeIfPresent(String.self, forKey: .imageCopyright)
        if let imageFormatListData = try container.decodeIfPresent([[String:MXMImageFormat]].self, forKey: .imageFormatList) {
            imageFormatList = imageFormatListData.compactMap{$0["image_format"]}
        } else {
            imageFormatList = nil
        }
    }

    public func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encode(imageId, forKey: .imageId)
        try container.encode(imageSourceId, forKey: .imageSourceId)
        try container.encodeIfPresent(imageAuthor, forKey: .imageAuthor)
        try container.encodeIfPresent(imageCopyright, forKey: .imageCopyright)
        if let imageFormatListData = imageFormatList {
            try container.encode(imageFormatListData.map{["image_format":$0]}, forKey: .imageFormatList)
        }
    }
}

struct MXMImageFormat : Codable, Equatable {
    let imageUrl : URL
    let imageFormatId, width, height : Int
}

Answer 2

Assuming MXMImageFormat is like this:

struct MXMImageFormat : Codable {
    let imageUrl: String
    let imageFormatId: Int
    let width: Int
    let height: Int
}

I think you are overthinking this. You can just do:

try imageFormatList?.forEach { imgFormat in
    var nested = imageContainer.nestedContainer(keyedBy: CodingKeys.ImageFormatListKey.self)
    try nested.encode(imgFormat, forKey: .imageFormat)
}

Since encode accepts any Encodable , including imgFormat . You don't actually need to convert to a Data first (at least that's why you seem to be attempting to do).

Some test code:

let json = """
{
   "image_id": 11101,
   "image_source_id": 9,
   "image_author": "",
   "image_copyright": "",
   "image_format_list": [{
           "image_format": {
               "image_url": "https://static.musixmatch.com/images-storage/mxmimages/1/0/1/1/1/11101_2.jpg",
               "image_format_id": 2,
               "width": 150,
               "height": 150
           }
       },
       {
           "image_format": {
               "image_url": "https://static.musixmatch.com/images-storage/mxmimages/1/0/1/1/1/11101_16.jpg",
               "image_format_id": 16,
               "width": 451,
               "height": 500
           }
       }
   ]
}
""".data(using: .utf8)!

let decoder = JSONDecoder()
decoder.keyDecodingStrategy = .convertFromSnakeCase
let model = try! decoder.decode(MXMImage.self, from: json)
let encoder = JSONEncoder()
encoder.keyEncodingStrategy = .convertToSnakeCase
let string = String(data: try! encoder.encode(model), encoding: .utf8)!
print(string) // this should be the same JSON as the one in the string literal

Also note that in encode , you don't have to use try? here:

while !imagesFormatListContainer.isAtEnd {
    let imageFormatContainer = try imagesFormatListContainer.nestedContainer(keyedBy: CodingKeys.ImageFormatListKey.self)
    // here vvvvvvv
    let imageFormat = try? imageFormatContainer.decode(MXMImageFormat.self, forKey: .imageFormat)
    if let imageFormat = imageFormat {
        imagesList.append(imageFormat)
    }
}