如何确保所有JSON字段都在Swift Decodable模型中显示？

Question

Let's imagine a third-party JSON API returning a model like this:

{
  "key1": "Hello"
}

So we describe it as follows:

struct Model: Codable {
  var key1: String
}

Eventually the JSON model gets a new field…

{
  "key1": "Hello",
  "key2": {
    "key3": "World"
  }
}

…and the old Model still works, but it misses a new property key2 .

Is there any way to verify that all JSON keys are presented in the Decodable model?

Answer 1

Here is a way to do it by getting all the keys in the json message by using JSONSerialization and then comparing them to the key(s) in the parsed data using reflection

This code only compares the count, a more thorough check should verify each individual key

do {
    let dictionary = try JSONSerialization.jsonObject(with: data) as? [String: Any]
    let result = try JSONDecoder().decode(Model.self, from: data)
    if let keys = dictionary?.keys {
        let mirror = Mirror(reflecting: result)
        if keys.count != mirror.children.count {
            print("Wrong number of keys") 
            //throw SomeError 
        } 
    }
    //handle result 
} catch {
    print(error)
}