Swift: Parsing a JSON file where you don't know the key values

Question

I'm building an app that queries wikidata using json. It works so far, but the issue I'm running into is the response I get from wikidata isn't the actual data, but an identifier. Then, to convert that identifier, I need to send it to another url and receive another json response, but the issue I'm running into is the the key value isn't something I know until I get the first json response in. So, lets say my key is Q1169621. When I run it through the api, I get this response:

I'm using codable and JSONDecoder, but I don't know how to tell the decoder the value of the key in entities is Q1169621 to get at the value I want ("Jim Lauderdale")...some of my code is below, I have structs to define the data of the response, but how do I replace the key value in my struct with the one defined from the previous json that is decoded?

struct InfoFromWikiConverted: Codable {
    
    let entities: Locator //this is the value I need to set before parsing the json
    
}

struct Locator: Codable {
    
    let labels: Labels //how do I link this to the struct above?
}

struct Labels: Codable {
    
    let en: EN
}

struct EN: Codable {
    
    let value: String
}

Decode a dictionary: `let entities: [String:Locator]` or write a custom initializer. — vadian, Aug 09 '20 at 05:01

score 1 · Answer 1 · answered Aug 09 '20 at 05:03

The simplest approach would be to decode entities as [String: Locator]:

struct InfoFromWikiConverted: Decodable {
   let entities: [String: Locator]
}

Of course, if you want your model to just be a single Locator (which means, potentially ignoring multiple keys under entities), then you'd need to manually decode it.

You'd need to create a type to represent any string Coding Key and implement init(from:):

struct InfoFromWikiConverted: Decodable {
   let entities: Locator
   
   struct CodingKeys: CodingKey {
      var stringValue: String
      var intValue: Int? = nil
        
      init(stringValue: String) { self.stringValue = stringValue }
      init?(intValue: Int) { return nil }
   }

   init(from decoder: Decoder) throws {
      let container = try decoder.container(keyedBy: CodingKeys.self)

      // get the first key (ignore the rest), and throw if there are none
      guard let key = container.allKeys.first else {
         throw DecodingError.dataCorrupted(
            .init(codingPath: container.codingPath, 
                  debugDescription: "Expected a non-empty object"))
      }

      let entities = try container.decode(Locator.self, forKey: key)
   }
}

Note that because you aren't retaining the ID, you can't encode it back to the same form, so I only conformed to Decodable instead of Codable

Swift: Parsing a JSON file where you don't know the key values

1 Answers1