[英]Decoding a generic decodable type
I need to create a generic struct that will hold any decodable type which is returned from the network, so I created something like this:我需要创建一个通用结构来保存从网络返回的任何可解码类型,所以我创建了这样的东西:
struct NetworkResponse<Wrapped: Decodable>: Decodable {
var result: Wrapped
}
so I can use the decoding method like this:所以我可以使用这样的解码方法:
struct MyModel: Decodable {
var id: Int
var name: String
var details: String
}
func getData<R: Decodable>(url: URL) -> AnyPublisher<R, Error>
URLSession.shared
.dataTaskPublisher(for: url)
.map(\.data)
.decode(type: NetworkResponse<R>.self, decoder: decoder)
.map(\.result)
.eraseToAnyPublisher()
//call site
let url = URL(string: "https://my/Api/Url")!
let models: [MyModel] = getData(url: url)
.sink {
//handle value here
}
But, I noticed that some responses from the network contains the result
key, and some others do not:但是,我注意到来自网络的一些响应包含
result
键,而另一些则不包含:
with result:结果:
{
"result": { [ "id": 2, "name": "some name", "details": "some details"] }
}
without result:没有结果:
[ "id": 2, "name": "some name", "details": "some details" ]
this results in the following error from the .map(\\.result)
publisher because it can't find the result
key in the returned json:这会导致
.map(\\.result)
发布者出现以下错误,因为它在返回的 json 中找不到result
键:
(typeMismatch(Swift.Dictionary<Swift.String, Any>, Swift.DecodingError.Context(codingPath: [], debugDescription: "Expected to decode Dictionary<String, Any> but found an array instead.", underlyingError: nil)))
How can I handle either case in the NetworkResponse
struct in order to avoid such error?我如何处理
NetworkResponse
结构中的任何一种情况以避免此类错误?
The JSON your posted isn't valid, but I'm assuming it's a typo and it's actually:您发布的 JSON 无效,但我假设这是一个错字,实际上是:
{ "id": 2, "name": "some name", "details": "some details" }
// or
{ "result": { "id": 2, "name": "some name", "details": "some details" } }
( {
}
instead of [
]
) (
{
}
而不是[
]
)
Probably the cleanest is with a manual decoder that can fall back to another type, if the first type fails:可能最干净的是使用手动解码器,如果第一种类型失败,可以回退到另一种类型:
struct NetworkResponse<Wrapped> {
let result: Wrapped
}
extension NetworkResponse: Decodable where Wrapped: Decodable {
private struct ResultResponse: Decodable {
let result: Wrapped
}
init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
do {
let result = try container.decode(ResultResponse.self)
self.result = result.result
} catch DecodingError.keyNotFound, DecodingError.typeMismatch {
self.result = try container.decode(Wrapped.self)
}
}
}
Alternatively, you can fall back within Combine.或者,您可以退回到 Combine 中。 I would not have gone with this approach, but for completeness-sake:
我不会采用这种方法,但为了完整性:
URLSession.shared
.dataTaskPublisher(for: url)
.map(\.data)
.flatMap { data in
Just(data)
.decode(type: NetworkResponse<R>.self, decoder: decoder)
.map(\.result)
.catch { _ in
Just(data)
.decode(type: R.self, decoder: decoder)
}
}
.eraseToAnyPublisher()
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