使用Decodable解码JSON嵌套字典并使用核心数据存储
我有以下使用Decodable解码JSON嵌套字典并使用核心数据存储,json,swift,core-data,decodable,Json,Swift,Core Data,Decodable,我有以下JSON结构: { "base": "USD", "date": "2020-04-24", "rates": { "CAD": 1.4049074074, "EUR": 0.9259259259 } } 我想将其解析为一个类并将其存储在核心数据中: class CurrencyRate: NSManagedObject, Decodable { enum CodingKeys: String, CodingKey { case
JSON
结构:
{
"base": "USD",
"date": "2020-04-24",
"rates": {
"CAD": 1.4049074074,
"EUR": 0.9259259259
}
}
我想将其解析为一个类并将其存储在核心数据中
:
class CurrencyRate: NSManagedObject, Decodable {
enum CodingKeys: String, CodingKey {
case base
case date
case rates
}
@NSManaged public var base: String
@NSManaged public var date: Date
@NSManaged public var rates: [String:Double]
required convenience init(from decoder: Decoder) throws {
...
}
根据我阅读的内容,为了在核心数据中存储费率
字段,我必须创建另一个这样的实体,并创建一对多关系:
class SubCurrencyRate: NSManagedObject, Decodable {
enum CodingKeys: String, CodingKey {
case currency
case rate
}
@NSManaged public var currency: String
@NSManaged public var rate: Double
required convenience init(from decoder: Decoder) throws {
...
}
而CurrencyRate
类中的rates
字段将是:@NSManaged public var rates:[SubCurrencyRate]
问题是我不知道如何将带有动态键的嵌套json解析到这些类中。怎样才能做到呢
一般来说,我如何解码JSON的这一部分:
"rates": {
"CAD": 1.4049074074,
"EUR": 0.9259259259
}
进入许多次货币比率
对象?我不久前写了一篇关于这方面的文章。
长话短说:我建议使用DTO解码到CoreData模型中。考虑到CoreData模型总是绑定到一个上下文(在从JSON解码时没有上下文),使用表示JSON的简单结构,然后从这些结构创建CoreData模型就更容易了。无需
次货币利率
符合可解码
,但您必须声明相反的关系(也在数据模型中!)
为了能够在核心数据中直接解析JSON,请声明两个扩展
extension CodingUserInfoKey {
static let context = CodingUserInfoKey(rawValue: "context")!
}
extension JSONDecoder {
convenience init(context: NSManagedObjectContext) {
self.init()
self.userInfo[.context] = context
}
}
在CurrencyRate
中,您必须在init中将对多关系声明为Set
(从decoder
解码费率字典并将其映射到SubCurrencyRate
实例。如果模型中正确定义了关系,则会自动填充属性以及反向关系
class CurrencyRate: NSManagedObject, Decodable {
enum CodingKeys: String, CodingKey { case base, date, rates }
@NSManaged public var base: String
@NSManaged public var date: Date
@NSManaged public var rates: Set<SubCurrencyRate>
required convenience init(from decoder: Decoder) throws {
guard let context = decoder.userInfo[.context] as? NSManagedObjectContext else { fatalError("Error: No object context!") }
let entity = NSEntityDescription.entity(forEntityName: "CurrencyRate", in: context)!
self.init(entity: entity, insertInto: context)
let values = try decoder.container(keyedBy: CodingKeys.self)
base = try values.decode(String.self, forKey: .base)
date = try values.decode(Date.self, forKey: .date)
let ratesData = try values.decode([String:Double].self, forKey: .rates)
for (key, value) in ratesData {
let subCurrencyRate = SubCurrencyRate(context: context)
subCurrencyRate.currency = key
subCurrencyRate.rate = value
subCurrencyRate.currencyRate = self
}
}
}
class CurrencyRate:NSManagedObject,可解码{
枚举编码键:字符串,编码键{案例库,日期,速率}
@NSManaged公共变量基:字符串
@NSV管理的公共var日期:日期
@NSM管理的公共风险值比率:设置
必需的便利初始化(来自解码器:解码器)抛出{
guard let context=decoder.userInfo[.context]as?NSManagedObjectContext else{fatalError(“错误:没有对象上下文!”)}
让entity=NSEntityDescription.entity(在:context中名为“CurrencyRate”)!
init(实体:实体,插入到:上下文)
let values=try decoder.container(keyedBy:CodingKeys.self)
base=try values.decode(String.self,forKey:.base)
日期=尝试值。解码(date.self,forKey:.date)
let ratesData=try values.decode([String:Double].self,forKey:.rates)
对于ratesData中的(键、值){
let subCurrencyRate=subCurrencyRate(上下文:上下文)
subCurrencyRate.currency=关键字
次货币比率。比率=值
subCurrencyRate.currencyRate=self
}
}
}
要解码JSON,您必须在传递托管对象上下文的扩展中使用
JSONDecoder(上下文:
API),要正确解码date
,您必须在创建新实体和添加关系时添加适当的dateDecodingStrategy
,您不需要为此添加特定属性(费率)因为该关系将充当汇率的属性。从建模的角度来看,最好将数据分解为货币对和汇率,然后只需要一个实体。
class CurrencyRate: NSManagedObject, Decodable {
enum CodingKeys: String, CodingKey { case base, date, rates }
@NSManaged public var base: String
@NSManaged public var date: Date
@NSManaged public var rates: Set<SubCurrencyRate>
required convenience init(from decoder: Decoder) throws {
guard let context = decoder.userInfo[.context] as? NSManagedObjectContext else { fatalError("Error: No object context!") }
let entity = NSEntityDescription.entity(forEntityName: "CurrencyRate", in: context)!
self.init(entity: entity, insertInto: context)
let values = try decoder.container(keyedBy: CodingKeys.self)
base = try values.decode(String.self, forKey: .base)
date = try values.decode(Date.self, forKey: .date)
let ratesData = try values.decode([String:Double].self, forKey: .rates)
for (key, value) in ratesData {
let subCurrencyRate = SubCurrencyRate(context: context)
subCurrencyRate.currency = key
subCurrencyRate.rate = value
subCurrencyRate.currencyRate = self
}
}
}