You can always write encode(to:) yourself, so you're not prevented from doing this. A setting across all of JSONEncoder would be much less flexible.

cc @itaiferber in case he has anything to add

Comment by Peter de Kraker (JIRA)

Yes, I understand that it can be done manually, but in my use case, and probably for a lot of other people, I have a API with lots of inputtypes, that I just want to match with simple data classes. To manually code the encode of everyone is a lot of work, and that's where Swift could (and should 🙂 ) make it easier on the developer. Especially because removing nils afterwards is easy, adding them is not.

Why assume that API's dont take nulls in JSON? Isn't that a bit unrealistic?

The assumption isn't necessarily just that APIs don't take nulls, but also that many treat null and absent as interchangeable, and that smaller payloads are better. If Swift is both the encoder and the decoder, for example, both of these are the case.

Comment by Sergey Balalaev (JIRA)

I think it's would be better, if we take a option as DateEncodingStrategy something like that: OptionalEncodingStrategy.

Comment by Mukesh (JIRA)

Would second sof.bix (JIRA User). For example rest api's have PATCH method, where only partial body is sent and if nulls are discarded, there wouldn't be a way to make an value null once it has been entered even if it optional.

Comment by Jon M Snyder (JIRA)

The difference between a client of an API knowing about something and setting it to null and not including the key at all can be important in many situations. Being able to still leverage all the goodness of Encodable and just tweak this behavior would be wonderful.

Comment by Jens Miltner (JIRA)

I would also like to second sof.bix (JIRA User) - not always are we in control of both frontend and backend and if backend treats null values and missing values differently, it's currently a pain to have to add a custom encode(to🙂 just to encode those null values (especially if there are a lot of different structs)

Comment by Nicolai Cornelis (JIRA)

I was pretty surprised to find that nils simply get thrown away as if they're meaningless. This is not really a great design choice in my opinion. The main benefit of using Encodable/Decodable is that you don't have to write all of the code for serialisation. Now we have to do it anyway if we have situations where an API expects null - or where null means something different than absent. This could be "change this property to null" vs. "don't change this property".

I like Sergey's suggestion. Please take another look at this.

Comment by Johan Nordberg (JIRA)

I also second Sergey's OptionalEncodingStrategy suggestion.

There is a third-party JSONEncoder in FineJSON that allows you to encode Optionals as null as a workaround until that lands.

EDIT: Just in case someone else who reads this tries to implement a custom Encoder that handles nil values. This might be obvious for people more familiar with Swift's type system but it took me for a spin: You need to implement all 13 specialized versions of KeyedEncodingContainerProtocol's encodeIfPresent it's not enough to just implement the generic version like you can do with encode.

Comment by Ben D. Jones (JIRA)

@swift-ci sync

Comment by Nicolai Cornelis (JIRA)

Hello

Any updates on this? This is currently quite the headache for us.

This is a huge issue for my team as well, as our back end uses explicit nil values for certain purposes.

Comment by Steven Grosmark (JIRA)

As a work-around, I've been using a property wrapper, along the lines of:

@propertyWrapper
public struct NullCodable<Wrapped: Encodable>: Encodable {
  public var wrappedValue: Wrapped?

  public func encode(to encoder: Encoder) throws {
    var container = encoder.singleValueContainer()
    switch wrappedValue {
    case .some(let value): try value.encode(to: encoder)
    case .none: try container.encodeNil()
  }
}

struct Test: Encodable {
  @NullCodable var name: String? = nil
}

JSONEncoder().encode(Test()) // -> "{\"name\": null}"

Not ideal, since each optional property needs to be marked, but it is a little easier than trying to implement a custom encoder.

I created a small package for it here: NullCodable.

Comment by Marcin Iwanicki (JIRA)

There are pros and cons of both cases.

Omitting optional properties results in a smaller payload. JSON format is frequently used in the networking layer as such the size of the payload matters.

I think it would be great to preserve the current behavior as default and avoid breaking changes. Adding a new property e.g. nilEncodingStrategy with options like skip (default), and includeNulls would work well, and be consistent with other options e.g. dataEncodingStrategy, dateEncodingStrategy.
As an alternative, it could possibly leverage the existing outputFormatting property with a new flag e.g. withNulls.

One more Reason to stop developing in Swift and start using React to develop your Apps! I don't get it why Apple cannot implement this simple stuff like other Languages did it ...
The Solution from swift-ci is not working for our App.
Very frustrating!

This actually just caused us a pretty nasty bug. In our case we had a completed_at timestamp that's optional. The iOS app set it to null and did an API call to mark a record as not complete (think, unchecking a checkbox). We found that while the local SQLite in the app had a null completed_at, the server still had the old timestamp. Then we realized the key was being omitted.

The problem is, omitting the key conflicts with Ruby on Rails' Strong Parameters, which take the parameters provided in the request and then filter them through a whitelist. When used in conjunction with ActiveRecord's update method, omitted fields are treated as "no change" for an update.

Including the optional null keys in the JSON is helpful for a few reasons:

1. If clients are only sending fields that changed (an even smaller payload, as you mentioned payload size), there's less problems with stale reads writing back outdated values (2 people editing different fields of the same record or something). This isn't possible if omitted fields are treated as an explicit null.
2. As I add more fields to my API, I do not want old versions of our app to wipe out fields that it does not even know exist. If these null optional fields were included in the JSON, I would know that the app does know that this field exists, and is setting it to null. Right now we're forced to change a lot of JSON Encoders in our iOS app, or introduce forward-compatibility problems in our API by treating omitted keys as explicit nulls.

I really hope this gets added as a JSONEncoder option like encoder.nilEncodingStrategy = .includeKeyWithJsonNull but have the default as .omitKey to not introduce a breaking change. A few server API's I interface with treat missing keys and Json null differently, so for every model (and there are a lot) I have to implement the CodingKeys enum, then override the encode property for every model property. This produces a ton of boiler plate code. Please consider adding this option. Thank you!