Use Codable to parse an array of JSON objects but skip broken elements [duplicate]

Question

I am passing a bunch of objects from a JSON but it turns out some of them have an empty string instead of a URL. My model expects a valid URL and I would rather skip the non-conforming objects than make the URL property optional.

This turns out to not be that straight-forward. Is there a built-in way to skip non-decodable objects from an array?

That's weird then that my search this time didn't turn it up. — Alper
– Alper, Commented Sep 5, 2018 at 9:24

Alper · Accepted Answer · 2018-09-04 21:48:47Z

3

It turns out that this is an open problem with a ticket in Swift.

I implemented the workaround as posted there on my problem in the following way:

struct AnyCodable: Codable {}

struct Trending: Codable {
  var data: [Gif]

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

    var gifContainer = try container.nestedUnkeyedContainer(forKey: .data)

    var gifs = [Gif]()

    while !gifContainer.isAtEnd {
      if let gif = try? gifContainer.decode(Gif.self) {
        gifs.append(gif)
      } else {
        let skipped = try? gifContainer.decode(AnyCodable.self)
        print("Skipping one \(skipped)")
      }
    }

    self.data = gifs
  }
}

answered Sep 4, 2018 at 21:48

Alper

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2 Comments

mc7h Over a year ago

Came here to validate my own solution and found this. I can see it's been answered elsewhere, but this more succinctly answers the question. The only differences I had were this: struct AnyDecodable: Decodable {} and _ = try gifContainer.decode(AnyCodable.self) You want to remove the try? because you might find yourself in an infinite loop.

Alper Over a year ago

You want to remove the try? for the line with let skipped? I want a handle on it to be able to print it out, so it might be better to remove the try? and turn the entire thing into another if let?

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