Parsing different JSON feeds in Swift to the same Decodable struct

问题

I have two different JSON feeds,

{
 "uid":9018823,
 "lat":43.25394,
 "lng":-2.93844,
 "bike":false,
 "name":"02-STATION",
 "address":null,
 "spot":true,
 "number":3388,
 "bikes":3,
 "booked_bikes":0,
 "bike_racks":20,
 "free_racks":16
}

and

{
 "address":null,"last_updated":1580546431,
 "renting":1,"returning":1,"uid":"3348"},
 "free_bikes":17,
 "id":"0a0d9d6e93abd05548c672b60bfa9099",
 "latitude":40.677236,
 "longitude":-74.015665,
 "station_name":"Coffey St & Conover St",
 "timestamp":"2020-02-01T09:26:31.254000Z"
}

What I would like is to parse both feeds filling the following structure,


struct Places: Codable {

    var name: String
    let lat: Double
    let lng: Double
}

As I've seen I can do this using Decodable in the init(from decoder:Decoder) but I can't wrap my head around it and make it work.

回答1:

One way to solve this is to have a CodingKey enum for each json message type and then when trying to create a container using one enum we catch any error instead of throwing it and tries to create a container using the other enum

struct Places: Decodable {
    let name: String
    let lat: Double
    let lng: Double

    enum CodingKeys1: String, CodingKey {
        case name
        case lat
        case lng
    }

    enum CodingKeys2: String, CodingKey {
        case name = "station_name"
        case lat = "latitude"
        case lng = "longitude"
    }

    init(from decoder: Decoder) throws {
        do {
            let container = try decoder.container(keyedBy: CodingKeys1.self)
            try self.init(container)
        } catch {
            let container = try decoder.container(keyedBy: CodingKeys2.self)
            try self.init(container)
        }
    }

    private init(_ container: KeyedDecodingContainer<CodingKeys1>) throws {
        name = try container.decode(String.self, forKey: .name)
        lat = try container.decode(Double.self, forKey: .lat)
        lng = try container.decode(Double.self, forKey: .lng)
    }

    private init(_ container: KeyedDecodingContainer<CodingKeys2>) throws {
        name = try container.decode(String.self, forKey: .name)
        lat = try container.decode(Double.self, forKey: .lat)
        lng = try container.decode(Double.self, forKey: .lng)
    }
}

Maybe the last part can be rewritten using generics.

Here is an example where data1 and data2 are the two samples from the question

do {

    for data in [data1, data2] {
        let result = try JSONDecoder().decode(Places.self, from: data)
        print(result)
    }
} catch {
    print(error)
}

Places(name: "02-STATION", lat: 43.25394, lng: -2.93844)
Places(name: "Coffey St & Conover St", lat: 40.677236, lng: -74.015665)

来源：https://stackoverflow.com/questions/60015691/parsing-different-json-feeds-in-swift-to-the-same-decodable-struct

标签

json

swift

decodable