How to parse JSON in Swift with dynamic filename using Codable - json

Question

I am trying to parse the following JSON into a class, but don't know how to approach this particular case.
Here is the api: https://en.wikipedia.org/w/api.php?format=json&action=query&prop=extracts&exintro=&explaintext=&indexpageids&titles=bird
I am trying to get the title and extract, but in order to do so, it requires that I go through the unique pageid. How would I do this using the Codable protocol?
{
"batchcomplete": "",
"query": {
"normalized": [
{
"from": "bird",
"to": "Bird"
}
],
"pageids": [
"3410"
],
"pages": {
"3410": {
"pageid": 3410,
"ns": 0,
"title": "Bird",
"extract": "..."
}
}
}
}

Answer 1

My suggestion is to write a custom initializer:
Decode pages as [String:Page] dictionary and map the inner dictionaries according to the values in pageids
let jsonString = """
{
"batchcomplete": "",
"query": {
"normalized": [
{
"from": "bird",
"to": "Bird"
}
],
"pageids": [
"3410"
],
"pages": {
"3410": {
"pageid": 3410,
"ns": 0,
"title": "Bird",
"extract": "..."
}
}
}
}
"""
struct Root : Decodable {
let query : Query
}
struct Query : Decodable {
let pageids : [String]
let pages : [Page]
private enum CodingKeys : String, CodingKey { case pageids, pages }
init(from decoder : Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
self.pageids = try container.decode([String].self, forKey: .pageids)
let pagesData = try container.decode([String:Page].self, forKey: .pages)
self.pages = self.pageids.compactMap{ pagesData[$0] }
}
}
struct Page : Decodable {
let pageid, ns : Int
let title, extract : String
}
let data = Data(jsonString.utf8)
do {
let result = try JSONDecoder().decode(Root.self, from: data)
print(result)
} catch {
print(error)
}