Type coercion in JSON serialization

[stevenschobert]

When working with models toJson and fromJson serializers, there is inconsistent behavior when it comes to the typed fields.

The model itself gets returned as a standard Object, but the model's fields preserve their original type.

In cases where you the field is one of the standard types (string, number, etc.), this isn't a problem.

The problem arrises when you deal with types like:

• Date
• ObjectID
• other models
• etc.

All these types will end up being converted to some other type by JSON.stringify, but I believe the developer experience will be more consistent if this conversion happens at the model level.

Example of Problem

// example model
@Model()
class Tweet extends SapiModelMixin() {
  @Json()
  content: string;
  @Json()
  postedDate: Date;
}

// example instance
let t = new Tweet();
t.content = "Hello world!";
t.postedDate = new Date();
await t.save();

// serialize to json does not convert types
let json = t.toJson();
console.log(typeof json.postedDate); // => Date
console.log(typeof json.id); // => ObjectID

// serialize from json does not convert types
let newTweet = Tweet.fromJSON({
  content: "hello 2",
  postedDate: "2018-03-28T20:24:13.960Z"
});
console.log(typeof newTweet.postedDate); // => string

Notes

If we decided to have the toJson and fromJson serialization do type conversion, we might have a convenient place to place some other conveniences, namely to support TypeScript's enum type, and serialize that to the enums string name.