Skipping empty string with JSONEncoders swift

Question

I a codable serialization extension which I use to turn my Codable struct to dictionaries, the problem I am facing is strings. I get string value from my UITextField at at times this value could be empty and as a result an empty string is decoded. How can I return nil if the value is an empty string.

extension Encodable {
    var requestDictionary: [String: Any]? {
        let encoder = JSONEncoder()
        encoder.keyEncodingStrategy = .convertToSnakeCase
        guard let data = try? encoder.encode(self) else { return nil }
        
        
        return (try? JSONSerialization.jsonObject(with: data, options: .allowFragments)).flatMap { $0 as? [String: Any] }
    }
}

if I have a Struct

let example = Exa(age: 10, name: "")
let dict = example.requestDictionary
print(dict)

I want it to just print ["age": 10] and return nil for the empty string

fix that in Exa init? self.name = name.isEmpty ? nil : name. By the way, why do you encode to JSON and then decode it again into a dictionary? — Sulthan
– Sulthan, Commented Oct 7, 2020 at 10:38
Because I am using a codable object and making an API call with dictionary parameters. — King
– King, Commented Oct 7, 2020 at 10:40
you cant customize inside a general extension so you have to make it inside the struct itself — Shehata Gamal
– Shehata Gamal, Commented Oct 7, 2020 at 10:44

Mario Huizinga · Accepted Answer · 2021-08-25 13:15:31Z

2

You can implement your own String encoding method extending KeyedEncodingContainer:

extension KeyedEncodingContainer {
    mutating func encode(_ value: String, forKey key: K) throws {
        guard !value.isEmpty else { return }
        try encodeIfPresent(value, forKey: key)
    }
}

Btw your request dictionary can be simplified as:

extension Encodable {
    var dictionary: [String: Any]? {
        let encoder = JSONEncoder()
        encoder.keyEncodingStrategy = .convertToSnakeCase
        return try? JSONSerialization.jsonObject(with: encoder.encode(self)) as? [String: Any]
    }
}

Playground testing:

struct Exa: Encodable {
    let age: Int
    let name: String
}

let example = Exa(age: 10, name: "")
let dict = example.dictionary!
print(dict)  // "["age": 10]\n"

edited Aug 25, 2021 at 13:15

Mario Huizinga

8268 silver badges16 bronze badges

answered Oct 7, 2020 at 17:16

Leo Dabus

237k61 gold badges512 silver badges624 bronze badges

Sign up to request clarification or add additional context in comments.

7 Comments

Mario Huizinga Over a year ago

This fails when a String property is not empty, e.g. let example = Exa(age: 10, name: "Leo"). The func encode keeps calling itself in an infinite loop.

Leo Dabus Over a year ago

@MarioHuizinga that is really weird. Not sure why would it cause a loop.

Mario Huizinga Over a year ago

I have tried exactly your example on Playground, just changing the name. Did you try that? It seems that the try encode(value, forKey: key) statement calls itself again (and again).

Leo Dabus Over a year ago

@MarioHuizinga yes I did notice that

Mario Huizinga Over a year ago

I fixed your solution by replacing try encode with try encodeIfPresent. This prevents the recursion. It works great now, thanks for this idea. I have submitted an Edit on your answer.

|

New Dev · Accepted Answer · 2020-10-07 15:48:41Z

I'll just another approach using a property wrapper to mark which properties could be skipped.

@propertyWrapper
struct SkipEmpty {
   var wrappedValue: String
}

extension SkipEmpty: Codable {
   init(from decoder: Decoder) throws {
      let container = try decoder.singleValueContainer()
      self.wrappedValue = try container.decode(String.self)
   }

   func encode(to encoder: Encoder) throws {
      // nothing to do here, see below
   }
}

But to actually skip, you'd also need to create a overload for the KeyedEncodingContainer.encode method for the SkipEmpty type:

extension KeyedEncodingContainer {
   mutating func encode(_ value: SkipEmpty, forKey key: K) throws {
      if !value.wrappedValue.isEmpty {
         try encode(value.wrappedValue, forKey: key) // encode the value here
      }
   }
}

You could possibly try to make it more generic, e.g. SkipEmpty<T: Codable> and provide another argument for the value to skip or a predicate, etc...

The usage is:

struct Exa: Encodable {
   var age: Int
   @SkipEmpty var name: String
}

Collectives™ on Stack Overflow

Skipping empty string with JSONEncoders swift

2 Answers 2

7 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

7 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related