Modify JSON key inside toJson

[CobeyH]

I have a question that pertains to Freezed used with Json_serializable.

I created this freezed class that contains several attributes that are custom classes, such as origin and assignee. The backend provides the entire json for these classes and they are correctly decoding using their own fromJson factories.

class LoadingList with _$LoadingList {
  const LoadingList._();
  factory LoadingList({
    String? uuid,
    required String name,
    Project? origin,
    User? assignee,
  }) = _LoadingList;

When one of these properties is changed in the frontend I need to update the backend with the new value. However, the backend doesn't accept the entire assignee object. It instead wants a json key called "assignee_id" that contains the uuid property from the assignee.

As an example, when the data is requested from the backend it would look like this:

{"uuid": "123", "name": "Test List", "origin": {"uuid": "456", ... }, "assignee": {"uuid": "789", ... } }

And when I send the request to update the LoadingList it would look like this:

{"uuid": "123", "name": "Test List 2", "origin_id": "876", "assignee_id": "971" }

If the keys of the json were the same when encoding/decoding then it wouldn't be a problem. I could created a JsonConverter that extracts the origin.uuid from the origin object when the LoadingList is encoded. However, I don't see a way to modify the keys of the json inside the toJson function. Ideally I'd remove the origin key and add the origin_id key.

All of my custom properties use the same format. They all need the key changed from property -> property_id and they need a value of property.uuid.

[CobeyH]

I found a solution that almost works. I created a separate property for each of my non-symetric types. Then I updated the includeToJson and includeFromJson properties so that the origin is read from the server and origin_id is sent to the server. However, this doesn't work because the originToJson function must be static, and I can't access the origin of my LoadingList within a static function.

 @protected
 @JsonKey(includeFromJson: false, toJson: originToJson)
 String? originId
 
  static String? _originToJson(_) => origin?.uuid;

I can't find a way for Freezed to serialize a computed value IE
String get originId => origin.uuid

So how can I assign the originId property either automatically when the origin changes or when the toJson function is called? I don't want to maintain origin and originId separately.