How do I fix the error described during json parsing using combine?-CodePudding

I'm trying to parse stock data from the website alphavantage.com using the combine frame work. I keep getting this error Swift.DecodingError.Context(codingPath: [], debugDescription: "No value associated with key CodingKeys(stringValue: \"bestMatches\", intValue: nil) (\"bestMatches\").", underlyingError: nil)) despite my data model having the correct values to match during with the json. How do I fix this ?

struct SearchResults: Decodable{
    let bestMatches : [SearchResult]
    
    enum CodingKeys: String, CodingKey{
        case bestMatches =  "bestMatches"
    }
}

struct SearchResult : Decodable{
    let symbol : String?
    let name : String?
    let type : String?
    let currency :String?
    
    enum CodingKeys:String, CodingKey{
       case symbol = "1. symbol"
       case  name = "2. name"
       case type = "3. type"
       case currency = "8. currency"
    }
}

struct APIservice{
    let apiKey = "U893NJLDIREGERHB"
    
    func fetchSymbols(keyword:String)-> AnyPublisher<SearchResults,Error>{
        let urlSTring = "https://www.alphavantage.co/query?function=\(keyword)H&keywords=tesco&apikey=U893NJLDIREGERHB"
        let url = URL(string: urlSTring)!
        return URLSession.shared.dataTaskPublisher(for: url)
            .map({$0.data})
            .decode(type: SearchResults.self, decoder: JSONDecoder())
            .receive(on: RunLoop.main)
            .eraseToAnyPublisher()
    }
}

   func performSearch(){
        apiSerivice.fetchSymbols(keyword: "S&P500").sink { (completion) in
            switch completion {
            case .failure(let error):
                print(error)
            case . finished:
                break
            }
        } receiveValue: { (SearchResults) in
            print(SearchResults.bestMatches)
        }.store(in: &subcribers)

CodePudding user response：

Your query is incorrect. Checking the documentation for symbol search, your URL must pass in SYMBOL_SEARCH for the function query.

Your query for the keyword was also not URL encoded as it should be, so "S&P 500" had the issue that it creates an invalid query when string interpolated. The better way would be to use URLComponents so this is handled for you safely.

Code:

func fetchSymbols(keyword: String) -> AnyPublisher<SearchResults, Error> {
    guard var components = URLComponents(string: "https://www.alphavantage.co/query") else {
        return Fail(
            outputType: SearchResults.self,
            failure: APIError.invalidComponents
        ).eraseToAnyPublisher()
    }
    components.queryItems = [
        URLQueryItem(name: "function", value: "SYMBOL_SEARCH"),
        URLQueryItem(name: "keywords", value: keyword),
        URLQueryItem(name: "apikey", value: apiKey)
    ]

    guard let url = components.url else {
        return Fail(
            outputType: SearchResults.self,
            failure: APIError.invalidURL
        ).eraseToAnyPublisher()
    }

    return URLSession.shared.dataTaskPublisher(for: url)
        .map(\.data)
        .decode(type: SearchResults.self, decoder: JSONDecoder())
        .receive(on: RunLoop.main)
        .eraseToAnyPublisher()
}

enum APIError: Error {
    case invalidComponents
    case invalidURL
}

I changed the query from "S&P500" to "S&P 500" because otherwise there are no results. You can also remove the redundant CodingKeys in SearchResults too because that has no effect.

Note: do not expose your API key!