การถอดรหัส JSON ต่างชนิด

JSON ต่างรูปแบบคืออะไร

import Foundation

let json = "[{\"type\":\"text\",\"value\":\"hi\"},{\"type\":\"number\",\"value\":42}]"
print("Each element carries a type discriminator")

การสร้างแบบจำลองด้วยชนิดแจกแจง

import Foundation

enum Block {
    case text(String)
    case number(Int)
}

print("Enum models the variants")

การกำหนดคีย์ตัวระบุชนิด

import Foundation

enum CodingKeys: String, CodingKey {
    case type
    case value
}

print(CodingKeys.type.stringValue, CodingKeys.value.stringValue)

การอ่านตัวระบุชนิด

import Foundation

enum Block: Decodable {
    case text(String)
    case number(Int)
    enum CodingKeys: String, CodingKey { case type, value }
    init(from decoder: Decoder) throws {
        let c = try decoder.container(keyedBy: CodingKeys.self)
        let type = try c.decode(String.self, forKey: .type)
        switch type {
        case "text": self = .text(try c.decode(String.self, forKey: .value))
        case "number": self = .number(try c.decode(Int.self, forKey: .value))
        default: throw DecodingError.dataCorruptedError(forKey: .type, in: c, debugDescription: "unknown type")
        }
    }
}

let b = try JSONDecoder().decode(Block.self, from: "{\"type\":\"text\",\"value\":\"hi\"}".data(using: .utf8)!)
if case let .text(s) = b { print(s) }

การถอดรหัสอาร์เรย์แบบผสม

import Foundation

enum Block: Decodable {
    case text(String)
    case number(Int)
    enum CodingKeys: String, CodingKey { case type, value }
    init(from decoder: Decoder) throws {
        let c = try decoder.container(keyedBy: CodingKeys.self)
        switch try c.decode(String.self, forKey: .type) {
        case "text": self = .text(try c.decode(String.self, forKey: .value))
        case "number": self = .number(try c.decode(Int.self, forKey: .value))
        default: throw DecodingError.dataCorruptedError(forKey: .type, in: c, debugDescription: "unknown")
        }
    }
}

let json = "[{\"type\":\"text\",\"value\":\"hi\"},{\"type\":\"number\",\"value\":42}]"
let blocks = try JSONDecoder().decode([Block].self, from: json.data(using: .utf8)!)
print(blocks.count)

การจับคู่รูปแบบของผลลัพธ์

import Foundation

enum Block: Decodable {
    case text(String)
    case number(Int)
    enum CodingKeys: String, CodingKey { case type, value }
    init(from decoder: Decoder) throws {
        let c = try decoder.container(keyedBy: CodingKeys.self)
        switch try c.decode(String.self, forKey: .type) {
        case "text": self = .text(try c.decode(String.self, forKey: .value))
        case "number": self = .number(try c.decode(Int.self, forKey: .value))
        default: throw DecodingError.dataCorruptedError(forKey: .type, in: c, debugDescription: "unknown")
        }
    }
}

let json = "[{\"type\":\"text\",\"value\":\"hi\"},{\"type\":\"number\",\"value\":42}]"
for b in try JSONDecoder().decode([Block].self, from: json.data(using: .utf8)!) {
    switch b {
    case .text(let s): print("text:", s)
    case .number(let n): print("number:", n)
    }
}

ข้อมูลที่ซ้อนกัน

import Foundation

struct ImagePayload: Decodable { var url: String; var width: Int }
enum Block: Decodable {
    case image(ImagePayload)
    enum CodingKeys: String, CodingKey { case type }
    init(from decoder: Decoder) throws {
        let c = try decoder.container(keyedBy: CodingKeys.self)
        switch try c.decode(String.self, forKey: .type) {
        case "image": self = .image(try ImagePayload(from: decoder))
        default: throw DecodingError.dataCorruptedError(forKey: .type, in: c, debugDescription: "unknown")
        }
    }
}

let json = "{\"type\":\"image\",\"url\":\"a.png\",\"width\":100}"
if case let .image(p) = try JSONDecoder().decode(Block.self, from: json.data(using: .utf8)!) {
    print(p.url, p.width)
}

การจัดการชนิดข้อมูลที่ไม่รู้จักอย่างเหมาะสม

import Foundation

enum Block: Decodable {
    case text(String)
    case unknown
    enum CodingKeys: String, CodingKey { case type, value }
    init(from decoder: Decoder) throws {
        let c = try decoder.container(keyedBy: CodingKeys.self)
        switch try c.decode(String.self, forKey: .type) {
        case "text": self = .text(try c.decode(String.self, forKey: .value))
        default: self = .unknown
        }
    }
}

let b = try JSONDecoder().decode(Block.self, from: "{\"type\":\"video\"}".data(using: .utf8)!)
if case .unknown = b { print("fell back to unknown") }

การเลือกตัวระบุชนิดที่ดี

import Foundation

enum Kind: String, Decodable { case text, number }

let data = "\"text\"".data(using: .utf8)!
let k = try JSONDecoder().decode(Kind.self, from: data)
print(k == .text)

การเข้ารหัสค่าหลายรูปแบบ

import Foundation

enum Block: Encodable {
    case text(String)
    case number(Int)
    enum CodingKeys: String, CodingKey { case type, value }
    func encode(to encoder: Encoder) throws {
        var c = encoder.container(keyedBy: CodingKeys.self)
        switch self {
        case .text(let s):
            try c.encode("text", forKey: .type)
            try c.encode(s, forKey: .value)
        case .number(let n):
            try c.encode("number", forKey: .type)
            try c.encode(n, forKey: .value)
        }
    }
}

let data = try JSONEncoder().encode(Block.number(42))
print(String(data: data, encoding: .utf8)!)

การประกอบทุกอย่างเข้าด้วยกัน

import Foundation

enum Block: Codable {
    case text(String)
    case number(Int)
    enum CodingKeys: String, CodingKey { case type, value }
    init(from d: Decoder) throws {
        let c = try d.container(keyedBy: CodingKeys.self)
        switch try c.decode(String.self, forKey: .type) {
        case "text": self = .text(try c.decode(String.self, forKey: .value))
        default: self = .number(try c.decode(Int.self, forKey: .value))
        }
    }
    func encode(to e: Encoder) throws {
        var c = e.container(keyedBy: CodingKeys.self)
        switch self {
        case .text(let s): try c.encode("text", forKey: .type); try c.encode(s, forKey: .value)
        case .number(let n): try c.encode("number", forKey: .type); try c.encode(n, forKey: .value)
        }
    }
}

let blocks: [Block] = [.text("hi"), .number(7)]
let data = try JSONEncoder().encode(blocks)
print(try JSONDecoder().decode([Block].self, from: data).count)

ตรวจความเข้าใจอย่างรวดเร็ว: JSON ต่างรูปแบบ

ทบทวน: การถอดรหัส JSON ต่างรูปแบบ