如何解析嵌套的JSON字符串作为Swift中的对象?
我有到位如何解析嵌套的JSON字符串作为Swift中的对象?
struct Symbol : Codable {
let id:Int
let type:String
let properties:[String:String]?
}
struct Event : Codable {
let event:String
let timestamp:Int
let symbol:Symbol?
}
struct LogRow : Codable {
let id:Int
let user_id:String
let question_id:String
let actions:[Event]
let timestamp:Double
}
和以下JSON阵列
[
{
"id": 26535754,
"user_id": "qhv1i39wsmbkzhjiffk1rrsg",
"question_id": "\"trapdoor|186752c1-948e-4c15-b3df-7d39a99fe9d6\"",
"actions": "[{\"event\": \"OPEN\", \"timestamp\": 1499802241640}, {\"event\": \"DRAG_START\", \"symbol\": {\"id\": 15, \"type\": \"Fn\", \"properties\": {\"name\": \"cos\", \"allowSubscript\": true, \"innerSuperscript\": true}}, \"timestamp\": 1499802243567}, {\"event\": \"UNDOCK_SYMBOL\", \"parent\": {\"id\": 14, \"type\": \"Fraction\"}, \"symbol\": {\"id\": 15, \"type\": \"Fn\", \"properties\": {\"name\": \"cos\", \"allowSubscript\": true, \"innerSuperscript\": true}}, \"timestamp\": 1499802243567, \"dockingPoint\": \"right\"}, {\"event\": \"DOCK_SYMBOL\", \"parent\": {\"id\": 13, \"type\": \"Fraction\"}, \"symbol\": {\"id\": 15, \"type\": \"Fn\", \"properties\": {\"name\": \"cos\", \"allowSubscript\": true, \"innerSuperscript\": true}}, \"timestamp\": 1499802243699, \"dockingPoint\": \"denominator\"}, {\"event\": \"DRAG_START\", \"symbol\": {\"id\": 16, \"type\": \"Num\", \"properties\": {\"significand\": \"60\"}}, \"timestamp\": 1499802244570}, {\"event\": \"UNDOCK_SYMBOL\", \"parent\": {\"id\": 15, \"type\": \"Fn\", \"properties\": {\"name\": \"cos\", \"allowSubscript\": true, \"innerSuperscript\": true}}, \"symbol\": {\"id\": 16, \"type\": \"Num\", \"properties\": {\"significand\": \"60\"}}, \"timestamp\": 1499802244570, \"dockingPoint\": \"argument\"}, {\"event\": \"DROP_SYMBOL\", \"symbol\": {\"id\": 16, \"type\": \"Num\", \"properties\": {\"significand\": \"60\"}}, \"timestamp\": 1499802245281}, {\"event\": \"DRAG_START\", \"symbol\": {\"id\": 13, \"type\": \"Fraction\"}, \"timestamp\": 1499802245845}, {\"event\": \"TRASH_SYMBOL\", \"symbol\": {\"id\": 13, \"type\": \"Fraction\"}, \"timestamp\": 1499802246826}, {\"event\": \"DRAG_START\", \"symbol\": {\"id\": 16, \"type\": \"Num\", \"properties\": {\"significand\": \"60\"}}, \"timestamp\": 1499802247468}, {\"event\": \"TRASH_SYMBOL\", \"symbol\": {\"id\": 16, \"type\": \"Num\", \"properties\": {\"significand\": \"60\"}}, \"timestamp\": 1499802248360}, {\"event\": \"DRAG_START\", \"symbol\": {\"id\": 19, \"type\": \"Num\", \"properties\": {\"significand\": \"2\"}}, \"timestamp\": 1499802249161}, {\"event\": \"UNDOCK_SYMBOL\", \"parent\": {\"id\": 14, \"type\": \"Fraction\"}, \"symbol\": {\"id\": 19, \"type\": \"Num\", \"properties\": {\"significand\": \"2\"}}, \"timestamp\": 1499802249161, \"dockingPoint\": \"denominator\"}, {\"event\": \"DOCK_SYMBOL\", \"parent\": {\"id\": 14, \"type\": \"Fraction\"}, \"symbol\": {\"id\": 19, \"type\": \"Num\", \"properties\": {\"significand\": \"2\"}}, \"timestamp\": 1499802249289, \"dockingPoint\": \"denominator\"}, {\"event\": \"DRAG_START\", \"symbol\": {\"id\": 19, \"type\": \"Num\", \"properties\": {\"significand\": \"2\"}}, \"timestamp\": 1499802249797}, {\"event\": \"UNDOCK_SYMBOL\", \"parent\": {\"id\": 14, \"type\": \"Fraction\"}, \"symbol\": {\"id\": 19, \"type\": \"Num\", \"properties\": {\"significand\": \"2\"}}, \"timestamp\": 1499802249797, \"dockingPoint\": \"denominator\"}, {\"event\": \"DOCK_SYMBOL\", \"parent\": {\"id\": 14, \"type\": \"Fraction\"}, \"symbol\": {\"id\": 19, \"type\": \"Num\", \"properties\": {\"significand\": \"2\"}}, \"timestamp\": 1499802249906, \"dockingPoint\": \"denominator\"}, {\"event\": \"DRAG_POTENTIAL_SYMBOL\", \"symbol\": {\"id\": 20, \"type\": \"Num\", \"properties\": {\"significand\": \"4\"}}, \"timestamp\": 1499802251451}, {\"event\": \"DROP_POTENTIAL_SYMBOL\", \"symbol\": {\"id\": 20, \"type\": \"Num\", \"properties\": {\"significand\": \"4\"}}, \"timestamp\": 1499802254229}, {\"event\": \"DRAG_START\", \"symbol\": {\"id\": 19, \"type\": \"Num\", \"properties\": {\"significand\": \"2\"}}, \"timestamp\": 1499802255231}, {\"event\": \"UNDOCK_SYMBOL\", \"parent\": {\"id\": 14, \"type\": \"Fraction\"}, \"symbol\": {\"id\": 19, \"type\": \"Num\", \"properties\": {\"significand\": \"2\"}}, \"timestamp\": 1499802255231, \"dockingPoint\": \"denominator\"}, {\"event\": \"TRASH_SYMBOL\", \"symbol\": {\"id\": 19, \"type\": \"Num\", \"properties\": {\"significand\": \"2\"}}, \"timestamp\": 1499802256593}, {\"event\": \"DRAG_START\", \"symbol\": {\"id\": 20, \"type\": \"Num\", \"properties\": {\"significand\": \"4\"}}, \"timestamp\": 1499802257376}, {\"event\": \"DOCK_SYMBOL\", \"parent\": {\"id\": 14, \"type\": \"Fraction\"}, \"symbol\": {\"id\": 20, \"type\": \"Num\", \"properties\": {\"significand\": \"4\"}}, \"timestamp\": 1499802258062, \"dockingPoint\": \"denominator\"}, {\"event\": \"CLOSE\", \"timestamp\": 1499802259093}]",
"timestamp": 1.499802259277E9
},
{
"id": 26535718,
"user_id": "qhv1i39wsmbkzhjiffk1rrsg",
"question_id": "\"trapdoor|186752c1-948e-4c15-b3df-7d39a99fe9d6\"",
"actions": "[{\"event\": \"OPEN\", \"timestamp\": 1499802175061}, {\"event\": \"DRAG_POTENTIAL_SYMBOL\", \"symbol\": {\"id\": 10, \"type\": \"Fraction\"}, \"timestamp\": 1499802178936}, {\"event\": \"DOCK_POTENTIAL_SYMBOL\", \"parent\": {\"id\": 7, \"type\": \"Symbol\", \"properties\": {\"letter\": \"g\"}}, \"symbol\": {\"id\": 10, \"type\": \"Fraction\"}, \"timestamp\": 1499802183785, \"dockingPoint\": \"subscript\"}, {\"event\": \"DRAG_START\", \"symbol\": {\"id\": 10, \"type\": \"Fraction\"}, \"timestamp\": 1499802184864}, {\"event\": \"UNDOCK_SYMBOL\", \"parent\": {\"id\": 7, \"type\": \"Symbol\", \"properties\": {\"letter\": \"g\"}}, \"symbol\": {\"id\": 10, \"type\": \"Fraction\"}, \"timestamp\": 1499802184865, \"dockingPoint\": \"subscript\"}, {\"event\": \"DOCK_SYMBOL\", \"parent\": {\"id\": 6, \"type\": \"Symbol\", \"properties\": {\"letter\": \"m\"}}, \"symbol\": {\"id\": 10, \"type\": \"Fraction\"}, \"timestamp\": 1499802185857, \"dockingPoint\": \"subscript\"}, {\"event\": \"DRAG_START\", \"symbol\": {\"id\": 10, \"type\": \"Fraction\"}, \"timestamp\": 1499802186710}, {\"event\": \"UNDOCK_SYMBOL\", \"parent\": {\"id\": 6, \"type\": \"Symbol\", \"properties\": {\"letter\": \"m\"}}, \"symbol\": {\"id\": 10, \"type\": \"Fraction\"}, \"timestamp\": 1499802186710, \"dockingPoint\": \"subscript\"}, {\"event\": \"DROP_SYMBOL\", \"symbol\": {\"id\": 10, \"type\": \"Fraction\"}, \"timestamp\": 1499802188430}, {\"event\": \"DRAG_POTENTIAL_SYMBOL\", \"symbol\": {\"id\": 11, \"type\": \"Fraction\"}, \"timestamp\": 1499802194665}, {\"event\": \"DROP_POTENTIAL_SYMBOL\", \"symbol\": {\"id\": 11, \"type\": \"Fraction\"}, \"timestamp\": 1499802195427}, {\"event\": \"DRAG_START\", \"symbol\": {\"id\": 6, \"type\": \"Symbol\", \"properties\": {\"letter\": \"m\"}}, \"timestamp\": 1499802196167}, {\"event\": \"DOCK_SYMBOL\", \"parent\": {\"id\": 11, \"type\": \"Fraction\"}, \"symbol\": {\"id\": 6, \"type\": \"Symbol\", \"properties\": {\"letter\": \"m\"}}, \"timestamp\": 1499802197167, \"dockingPoint\": \"numerator\"}, {\"event\": \"DRAG_START\", \"symbol\": {\"id\": 8, \"type\": \"Fn\", \"properties\": {\"name\": \"cos\", \"allowSubscript\": true, \"innerSuperscript\": true}}, \"timestamp\": 1499802198247}, {\"event\": \"UNDOCK_SYMBOL\", \"parent\": {\"id\": 7, \"type\": \"Symbol\", \"properties\": {\"letter\": \"g\"}}, \"symbol\": {\"id\": 8, \"type\": \"Fn\", \"properties\": {\"name\": \"cos\", \"allowSubscript\": true, \"innerSuperscript\": true}}, \"timestamp\": 1499802198247, \"dockingPoint\": \"right\"}, {\"event\": \"DOCK_SYMBOL\", \"parent\": {\"id\": 11, \"type\": \"Fraction\"}, \"symbol\": {\"id\": 8, \"type\": \"Fn\", \"properties\": {\"name\": \"cos\", \"allowSubscript\": true, \"innerSuperscript\": true}}, \"timestamp\": 1499802199971, \"dockingPoint\": \"right\"}, {\"event\": \"DRAG_START\", \"symbol\": {\"id\": 11, \"type\": \"Fraction\"}, \"timestamp\": 1499802201551}, {\"event\": \"DROP_SYMBOL\", \"symbol\": {\"id\": 11, \"type\": \"Fraction\"}, \"timestamp\": 1499802202638}, {\"event\": \"DRAG_POTENTIAL_SYMBOL\", \"symbol\": {\"id\": 12, \"type\": \"Num\", \"properties\": {\"significand\": \"2\"}}, \"timestamp\": 1499802209025}, {\"event\": \"DOCK_POTENTIAL_SYMBOL\", \"parent\": {\"id\": 11, \"type\": \"Fraction\"}, \"symbol\": {\"id\": 12, \"type\": \"Num\", \"properties\": {\"significand\": \"2\"}}, \"timestamp\": 1499802210771, \"dockingPoint\": \"denominator\"}, {\"event\": \"CLOSE\", \"timestamp\": 1499802212398}]",
"timestamp": 1.49980221259E9
}
]
的JSON数据来自一个数据库,通过DataGrip的JSON出口导出的以下数据结构。数据库字段的类型是JSON Blob(它是Postgres,所以没关系)。查询是这样的:
SELECT
...
event_details->>'actions' AS actions,
...
FROM yadda_yadda...;
万一它是有用的(是的,我也试过单箭头版本,没有区别)。
我的问题是我该如何让Swift将actions
字符串解析为[Event]
作为JSON对象?或者,有没有办法使DataGrip(或Postgres)将该字段导出为对象而不是序列化的对象?
编辑我改变LogRow
这样
struct LogRow : Codable {
let id:Int
let user_id:String
let question_id:String
let actions:[Event]
let timestamp:Double
enum CodingKeys: String, CodingKey {
case id
case user_id
case question_id
case actions
case timestamp
}
init(from decoder: Decoder) throws {
let values = try decoder.container(keyedBy: CodingKeys.self)
id = try values.decode(Int.self, forKey: .id)
user_id = try values.decode(String.self, forKey: .user_id)
question_id = try values.decode(String.self, forKey: .question_id)
timestamp = try values.decode(Double.self, forKey: .timestamp)
let actions_string = try values.decode(String.self, forKey: .actions)
let actions_data = actions_string.data(using: .utf8)!
actions = try JSONDecoder().decode([Event].self, from: actions_data)
}
}
,现在我得到一个类似的错误之前,但显然对Event
,而不是在LogRow
了。
fatal error: Error raised at top level:
Swift.DecodingError.typeMismatch(Swift.String,
Swift.DecodingError.Context(codingPath: [Foundation.(_JSONKey in
_12768CA107A31EF2DCE034FD75B541C9)(stringValue: "Index 1", intValue:
Optional(1)), tree_builder.Event.(CodingKeys in
_D5964B2C6A943A986EE24818C2C63D9B).symbol, tree_builder.Symbol.
(CodingKeys in _D5964B2C6A943A986EE24818C2C63D9B).properties,
Swift._DictionaryCodingKey(stringValue: "allowSubscript", intValue:
nil)], debugDescription: "Expected to decode String but found a number
instead.", underlyingError: nil)): file
/Library/Caches/com.apple.xbs/Sources/swiftlang/swiftlang-
900.0.65/src/swift/stdlib/public/core/ErrorType.swift, line 187
您可以使用可选的链接,这是由苹果公司提供的解决方案:https://developer.apple.com/swift/blog/?id=37
还有库,它会为你,就像https://github.com/Hearst-DD/ObjectMapper,或https://github.com/tristanhimmelman/AlamofireObjectMapper
这是一个基本的例子如何做到这一点,但你应该重构,并看看我给的链接:
guard let event = jsonObject["event"] as? String, let timestamp = jsonObject["timestamp"] as? Int else {return}
myEvent.event = event
myEvent.timestamp = timestamp
if let symbol = jsonObject["symbol"] as? [String:Any] {
guard let symbolId = symbol["id"] as? Int, let type = symbol["type"] else {return}
let mySymbol = symbol()
mySymbol.id = id
mySymbol.type = type
}
编辑
如果您正在使用SWIFT 4和可编码协议,它应该是很容易的,你就必须让你的嵌套对象为可编码的呢!然后只是:
try decoder.decode(yourType.self, from: yourJsonString)
如果您正确使用CodingKeys它应该这样做。
Uuuh,我的问题不是如何将json字符串解码为对象。如果我将一个测试字符串提供给解码器并要求它吐出一个'Event'对象,那么这会起作用。我的问题是:假设序列化的LogRow包含一个字符串,该字符串包含在其“actions”键中的一个“Event”数组的序列化表示,如何使解码器对该字符串进行反序列化并将其转换为“ Event's? – Morpheu5
https://developer.apple.com/documentation/foundation/archives_and_serialization/encoding_and_decoding_custom_types –
问题在于properties
的声明,因为JSON对象不会对[String:String]
字典进行编码,因为某些值可能不是String
s。所以,这是这个问题的“答案”,但这并不能解决嵌套问题,所以我创建了一个新问题:How do I parse a JSON object that has type-dependent sub-objects, in Swift?
首先,你应该摆脱所有这些隐式解包的optionals。这个答案告诉你如何完成它https://*.com/a/43121890/2303865 –
我通常会,但在这种情况下,我绝对肯定我可以隐式解开我的选择权,因为我完全控制环境,包括数据集。如果我要在野外释放它,我肯定会摆脱这一点。 – Morpheu5
这是不是,如果你可以或不可以。你不需要它。 –