使用值有时是 Int 有时是 String 的 codable
Using codable with value that is sometimes an Int and other times a String
我有一个 API 有时会 return 一个特定的键值(在本例中是 id
)在 JSON 中作为一个 Int 有时它会return 与字符串相同的键值。我如何使用 codable 来解析 JSON?
struct GeneralProduct: Codable {
var price: Double!
var id: String?
var name: String!
private enum CodingKeys: String, CodingKey {
case price = "p"
case id = "i"
case name = "n"
}
init(price: Double? = nil, id: String? = nil, name: String? = nil) {
self.price = price
self.id = id
self.name = name
}
}
我不断收到此错误消息:Expected to decode String but found a number instead
。它 return 是一个数字的原因是因为 id 字段为空,当 id 字段为空时,它默认为 returning 0 作为 ID,codable 将其标识为数字。我基本上可以忽略 ID 密钥,但据我所知,codable 没有给我忽略它的选项。处理此问题的最佳方法是什么?
这里是JSON。超级简单
工作
{
"p":2.12,
"i":"3k3mkfnk3",
"n":"Blue Shirt"
}
错误 - 因为系统中没有 id,它 returns 0 作为默认值,codable 显然将其视为与字符串相对的数字。
{
"p":2.19,
"i":0,
"n":"Black Shirt"
}
struct GeneralProduct: Codable {
var price: Double?
var id: String?
var name: String?
private enum CodingKeys: String, CodingKey {
case price = "p", id = "i", name = "n"
}
init(price: Double? = nil, id: String? = nil, name: String? = nil) {
self.price = price
self.id = id
self.name = name
}
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
price = try container.decode(Double.self, forKey: .price)
name = try container.decode(String.self, forKey: .name)
do {
id = try String(container.decode(Int.self, forKey: .id))
} catch DecodingError.typeMismatch {
id = try container.decode(String.self, forKey: .id)
}
}
}
let json1 = """
{
"p":2.12,
"i":"3k3mkfnk3",
"n":"Blue Shirt"
}
"""
let json2 = """
{
"p":2.12,
"i":0,
"n":"Blue Shirt"
}
"""
do {
let product = try JSONDecoder().decode(GeneralProduct.self, from: Data(json2.utf8))
print(product.price ?? "nil")
print(product.id ?? "nil")
print(product.name ?? "nil")
} catch {
print(error)
}
edit/update:
您也可以简单地将 nil
分配给您的 id
当您的 api returns 0
:
do {
let value = try container.decode(Int.self, forKey: .id)
id = value == 0 ? nil : String(value)
} catch DecodingError.typeMismatch {
id = try container.decode(String.self, forKey: .id)
}
这是 MetadataType
的一个可能解决方案,好处是它可以是一个通用解决方案,不仅适用于 GeneralProduct
,而且适用于所有具有相同歧义的 struct
:
struct GeneralProduct: Codable {
var price:Double?
var id:MetadataType?
var name:String?
private enum CodingKeys: String, CodingKey {
case price = "p"
case id = "i"
case name = "n"
}
init(price:Double? = nil, id: MetadataType? = nil, name: String? = nil) {
self.price = price
self.id = id
self.name = name
}
}
enum MetadataType: Codable {
case int(Int)
case string(String)
init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
do {
self = try .int(container.decode(Int.self))
} catch DecodingError.typeMismatch {
do {
self = try .string(container.decode(String.self))
} catch DecodingError.typeMismatch {
throw DecodingError.typeMismatch(MetadataType.self, DecodingError.Context(codingPath: decoder.codingPath, debugDescription: "Encoded payload not of an expected type"))
}
}
}
func encode(to encoder: Encoder) throws {
var container = encoder.singleValueContainer()
switch self {
case .int(let int):
try container.encode(int)
case .string(let string):
try container.encode(string)
}
}
}
这是测试:
let decoder = JSONDecoder()
var json = "{\"p\":2.19,\"i\":0,\"n\":\"Black Shirt\"}"
var product = try! decoder.decode(GeneralProduct.self, from: json.data(using: .utf8)!)
if let id = product.id {
print(id) // 0
}
json = "{\"p\":2.19,\"i\":\"hello world\",\"n\":\"Black Shirt\"}"
product = try! decoder.decode(GeneralProduct.self, from: json.data(using: .utf8)!)
if let id = product.id {
print(id) // hello world
}
如果您想从 Int
或 String
无缝解码,您需要某种包装器。
多亏了语言的(某种程度上)新添加(属性 包装器),您最终可以得到一些像这样的漂亮代码:
// note this is only `Decodable`
struct GeneralProduct: Decodable {
var price: Double
@Flexible var id: Int // note this is an Int
var name: String
}
属性包装器及其支持代码可以这样实现:
@propertyWrapper struct Flexible<T: FlexibleDecodable>: Decodable {
var wrappedValue: T
init(from decoder: Decoder) throws {
wrappedValue = try T(container: decoder.singleValueContainer())
}
}
protocol FlexibleDecodable {
init(container: SingleValueDecodingContainer) throws
}
extension Int: FlexibleDecodable {
init(container: SingleValueDecodingContainer) throws {
if let int = try? container.decode(Int.self) {
self = int
} else if let string = try? container.decode(String.self), let int = Int(string) {
self = int
} else {
throw DecodingError.dataCorrupted(.init(codingPath: container.codingPath, debugDescription: "Invalid int value"))
}
}
}
原回答
您可以在知道如何从任何基本 JSON 数据类型解码的字符串上使用包装器:字符串、数字、布尔值:
struct RelaxedString: Codable {
let value: String
init(_ value: String) {
self.value = value
}
init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
// attempt to decode from all JSON primitives
if let str = try? container.decode(String.self) {
value = str
} else if let int = try? container.decode(Int.self) {
value = int.description
} else if let double = try? container.decode(Double.self) {
value = double.description
} else if let bool = try? container.decode(Bool.self) {
value = bool.description
} else {
throw DecodingError.typeMismatch(String.self, .init(codingPath: decoder.codingPath, debugDescription: ""))
}
}
func encode(to encoder: Encoder) throws {
var container = encoder.singleValueContainer()
try container.encode(value)
}
}
然后您可以在您的结构中使用这个新类型。一个小缺点是该结构的使用者将需要进行另一个间接访问来访问包装的字符串。然而,这可以通过将解码的 RelaxedString
属性 声明为私有来避免,并为 public 接口使用计算的:
struct GeneralProduct: Codable {
var price: Double!
var _id: RelaxedString?
var name: String!
var id: String? {
get { _id?.value }
set { _id = newValue.map(RelaxedString.init) }
}
private enum CodingKeys: String, CodingKey {
case price = "p"
case _id = "i"
case name = "n"
}
init(price: Double? = nil, id: String? = nil, name: String? = nil) {
self.price = price
self._id = id.map(RelaxedString.init)
self.name = name
}
}
上述方法的优点:
- 无需编写自定义
init(from decoder: Decoder)
代码,如果要解码的属性数量增加,代码会变得乏味
- 可重用性 -
RelaxedString
可以在其他结构中无缝使用
- id 可以从字符串或 int 解码的事实仍然是一个实现细节,
GeneralProduct
的消费者不要 know/careid 可以来自 string 或 int
- public 接口公开了字符串值,这使得消费者代码变得简单,因为它不必处理多种类型的数据
我创建了这个 Gist,它有一个可以处理的 ValueWrapper 结构
以下类型
case stringValue(String)
case intValue(Int)
case doubleValue(Double)
case boolValue(Bool)
https://gist.github.com/amrangry/89097b86514b3477cae79dd28bba3f23
根据@Cristik 的回答,我提出了另一种使用 @propertyWrapper
的解决方案。
@propertyWrapper
struct StringForcible: Codable {
var wrappedValue: String?
enum CodingKeys: CodingKey {}
init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
if let string = try? container.decode(String.self) {
wrappedValue = string
} else if let integer = try? container.decode(Int.self) {
wrappedValue = "\(integer)"
} else if let double = try? container.decode(Double.self) {
wrappedValue = "\(double)"
} else if container.decodeNil() {
wrappedValue = nil
}
else {
throw DecodingError.typeMismatch(String.self, .init(codingPath: container.codingPath, debugDescription: "Could not decode incoming value to String. It is not a type of String, Int or Double."))
}
}
func encode(to encoder: Encoder) throws {
var container = encoder.singleValueContainer()
try container.encode(wrappedValue)
}
init() {
self.wrappedValue = nil
}
}
用法是
struct SomeDTO: Codable {
@StringForcible var id: String?
}
也像-我认为-
struct AnotherDTO: Codable {
var some: SomeDTO?
}
我有一个 API 有时会 return 一个特定的键值(在本例中是 id
)在 JSON 中作为一个 Int 有时它会return 与字符串相同的键值。我如何使用 codable 来解析 JSON?
struct GeneralProduct: Codable {
var price: Double!
var id: String?
var name: String!
private enum CodingKeys: String, CodingKey {
case price = "p"
case id = "i"
case name = "n"
}
init(price: Double? = nil, id: String? = nil, name: String? = nil) {
self.price = price
self.id = id
self.name = name
}
}
我不断收到此错误消息:Expected to decode String but found a number instead
。它 return 是一个数字的原因是因为 id 字段为空,当 id 字段为空时,它默认为 returning 0 作为 ID,codable 将其标识为数字。我基本上可以忽略 ID 密钥,但据我所知,codable 没有给我忽略它的选项。处理此问题的最佳方法是什么?
这里是JSON。超级简单
工作
{
"p":2.12,
"i":"3k3mkfnk3",
"n":"Blue Shirt"
}
错误 - 因为系统中没有 id,它 returns 0 作为默认值,codable 显然将其视为与字符串相对的数字。
{
"p":2.19,
"i":0,
"n":"Black Shirt"
}
struct GeneralProduct: Codable {
var price: Double?
var id: String?
var name: String?
private enum CodingKeys: String, CodingKey {
case price = "p", id = "i", name = "n"
}
init(price: Double? = nil, id: String? = nil, name: String? = nil) {
self.price = price
self.id = id
self.name = name
}
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
price = try container.decode(Double.self, forKey: .price)
name = try container.decode(String.self, forKey: .name)
do {
id = try String(container.decode(Int.self, forKey: .id))
} catch DecodingError.typeMismatch {
id = try container.decode(String.self, forKey: .id)
}
}
}
let json1 = """
{
"p":2.12,
"i":"3k3mkfnk3",
"n":"Blue Shirt"
}
"""
let json2 = """
{
"p":2.12,
"i":0,
"n":"Blue Shirt"
}
"""
do {
let product = try JSONDecoder().decode(GeneralProduct.self, from: Data(json2.utf8))
print(product.price ?? "nil")
print(product.id ?? "nil")
print(product.name ?? "nil")
} catch {
print(error)
}
edit/update:
您也可以简单地将 nil
分配给您的 id
当您的 api returns 0
:
do {
let value = try container.decode(Int.self, forKey: .id)
id = value == 0 ? nil : String(value)
} catch DecodingError.typeMismatch {
id = try container.decode(String.self, forKey: .id)
}
这是 MetadataType
的一个可能解决方案,好处是它可以是一个通用解决方案,不仅适用于 GeneralProduct
,而且适用于所有具有相同歧义的 struct
:
struct GeneralProduct: Codable {
var price:Double?
var id:MetadataType?
var name:String?
private enum CodingKeys: String, CodingKey {
case price = "p"
case id = "i"
case name = "n"
}
init(price:Double? = nil, id: MetadataType? = nil, name: String? = nil) {
self.price = price
self.id = id
self.name = name
}
}
enum MetadataType: Codable {
case int(Int)
case string(String)
init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
do {
self = try .int(container.decode(Int.self))
} catch DecodingError.typeMismatch {
do {
self = try .string(container.decode(String.self))
} catch DecodingError.typeMismatch {
throw DecodingError.typeMismatch(MetadataType.self, DecodingError.Context(codingPath: decoder.codingPath, debugDescription: "Encoded payload not of an expected type"))
}
}
}
func encode(to encoder: Encoder) throws {
var container = encoder.singleValueContainer()
switch self {
case .int(let int):
try container.encode(int)
case .string(let string):
try container.encode(string)
}
}
}
这是测试:
let decoder = JSONDecoder()
var json = "{\"p\":2.19,\"i\":0,\"n\":\"Black Shirt\"}"
var product = try! decoder.decode(GeneralProduct.self, from: json.data(using: .utf8)!)
if let id = product.id {
print(id) // 0
}
json = "{\"p\":2.19,\"i\":\"hello world\",\"n\":\"Black Shirt\"}"
product = try! decoder.decode(GeneralProduct.self, from: json.data(using: .utf8)!)
if let id = product.id {
print(id) // hello world
}
如果您想从 Int
或 String
无缝解码,您需要某种包装器。
多亏了语言的(某种程度上)新添加(属性 包装器),您最终可以得到一些像这样的漂亮代码:
// note this is only `Decodable`
struct GeneralProduct: Decodable {
var price: Double
@Flexible var id: Int // note this is an Int
var name: String
}
属性包装器及其支持代码可以这样实现:
@propertyWrapper struct Flexible<T: FlexibleDecodable>: Decodable {
var wrappedValue: T
init(from decoder: Decoder) throws {
wrappedValue = try T(container: decoder.singleValueContainer())
}
}
protocol FlexibleDecodable {
init(container: SingleValueDecodingContainer) throws
}
extension Int: FlexibleDecodable {
init(container: SingleValueDecodingContainer) throws {
if let int = try? container.decode(Int.self) {
self = int
} else if let string = try? container.decode(String.self), let int = Int(string) {
self = int
} else {
throw DecodingError.dataCorrupted(.init(codingPath: container.codingPath, debugDescription: "Invalid int value"))
}
}
}
原回答
您可以在知道如何从任何基本 JSON 数据类型解码的字符串上使用包装器:字符串、数字、布尔值:
struct RelaxedString: Codable {
let value: String
init(_ value: String) {
self.value = value
}
init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
// attempt to decode from all JSON primitives
if let str = try? container.decode(String.self) {
value = str
} else if let int = try? container.decode(Int.self) {
value = int.description
} else if let double = try? container.decode(Double.self) {
value = double.description
} else if let bool = try? container.decode(Bool.self) {
value = bool.description
} else {
throw DecodingError.typeMismatch(String.self, .init(codingPath: decoder.codingPath, debugDescription: ""))
}
}
func encode(to encoder: Encoder) throws {
var container = encoder.singleValueContainer()
try container.encode(value)
}
}
然后您可以在您的结构中使用这个新类型。一个小缺点是该结构的使用者将需要进行另一个间接访问来访问包装的字符串。然而,这可以通过将解码的 RelaxedString
属性 声明为私有来避免,并为 public 接口使用计算的:
struct GeneralProduct: Codable {
var price: Double!
var _id: RelaxedString?
var name: String!
var id: String? {
get { _id?.value }
set { _id = newValue.map(RelaxedString.init) }
}
private enum CodingKeys: String, CodingKey {
case price = "p"
case _id = "i"
case name = "n"
}
init(price: Double? = nil, id: String? = nil, name: String? = nil) {
self.price = price
self._id = id.map(RelaxedString.init)
self.name = name
}
}
上述方法的优点:
- 无需编写自定义
init(from decoder: Decoder)
代码,如果要解码的属性数量增加,代码会变得乏味 - 可重用性 -
RelaxedString
可以在其他结构中无缝使用 - id 可以从字符串或 int 解码的事实仍然是一个实现细节,
GeneralProduct
的消费者不要 know/careid 可以来自 string 或 int - public 接口公开了字符串值,这使得消费者代码变得简单,因为它不必处理多种类型的数据
我创建了这个 Gist,它有一个可以处理的 ValueWrapper 结构 以下类型
case stringValue(String)
case intValue(Int)
case doubleValue(Double)
case boolValue(Bool)
https://gist.github.com/amrangry/89097b86514b3477cae79dd28bba3f23
根据@Cristik 的回答,我提出了另一种使用 @propertyWrapper
的解决方案。
@propertyWrapper
struct StringForcible: Codable {
var wrappedValue: String?
enum CodingKeys: CodingKey {}
init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
if let string = try? container.decode(String.self) {
wrappedValue = string
} else if let integer = try? container.decode(Int.self) {
wrappedValue = "\(integer)"
} else if let double = try? container.decode(Double.self) {
wrappedValue = "\(double)"
} else if container.decodeNil() {
wrappedValue = nil
}
else {
throw DecodingError.typeMismatch(String.self, .init(codingPath: container.codingPath, debugDescription: "Could not decode incoming value to String. It is not a type of String, Int or Double."))
}
}
func encode(to encoder: Encoder) throws {
var container = encoder.singleValueContainer()
try container.encode(wrappedValue)
}
init() {
self.wrappedValue = nil
}
}
用法是
struct SomeDTO: Codable {
@StringForcible var id: String?
}
也像-我认为-
struct AnotherDTO: Codable {
var some: SomeDTO?
}